<PAGE>

===============================================================================

                                                                  EXHIBIT 10.5

                             RSL COMMUNICATIONS PLC
                                    As Issuer


                            RSL COMMUNICATIONS, LTD.
                                  As Guarantor

                              RSL COM U.S.A., INC.
                             As Subsidiary Guarantor


                                       TO
                            THE CHASE MANHATTAN BANK,
                                   As Trustee


                             ----------------------


                          SECOND SUPPLEMENTAL INDENTURE


                          Dated as of February 22, 2000


                             ----------------------


                            12% SENIOR NOTES DUE 2008


===============================================================================

<PAGE>

                          SECOND SUPPLEMENTAL INDENTURE

                  SECOND SUPPLEMENTAL INDENTURE, dated as of February 22, 2000
(the "Second Supplemental Indenture"), between RSL Communications PLC, a United
Kingdom corporation, as issuer (hereinafter called the "Issuer"), RSL
Communications, Ltd., a Bermuda corporation, as guarantor (hereinafter called
the "Guarantor"), RSL COM U.S.A., Inc., a Delaware corporation, as guarantor
(hereinafter called the "Subsidiary Guarantor"), and The Chase Manhattan Bank, a
corporation duly organized and existing under the laws of the State of New York,
as Trustee (hereinafter called the "Trustee").

                  Capitalized terms used herein but not otherwise defined herein
shall have the meanings given to such terms in the Indenture, dated as of
November 9, 1998, between the Company, the Guarantor and the Trustee (the
"Indenture").

                                    Recitals

                  WHEREAS, the Issuer, the Guarantor and the Trustee entered
into the Indenture pursuant to which the Issuer issued its 12% Senior Notes due
2008 (the "Securities");

                  WHEREAS, the Issuer desires to issue its euro denominated
senior notes due 2010 (the "Euro Notes") and its dollar denominated senior notes
due 2010 (the "Dollar Notes") in an aggregate principal amount of up to
approximately $230,000,000 (or the U.S. dollar equivalent);

                  WHEREAS, the Subsidiary Guarantor has substantially benefited
from the issuance of the Notes and expects to substantially benefit from the
issuance of the Dollar Notes and the Euro Notes;

                  WHEREAS, to facilitate the offering of the Dollar Notes and
the Euro Notes, the Subsidiary Guarantor is fully, unconditionally and
irrevocably guaranteeing, on an unsubordinated basis, all of the obligations of
the Issuer under the Dollar Notes, the Euro Notes and the indentures pursuant to
which they will be issued;

                  WHEREAS, Section 10.16 of the Indenture provides that the
Subsidiary Guarantor may not guarantee any Indebtedness of the Issuer unless the
Subsidiary Guarantor simultaneously executes and delivers a supplemental
indenture to the Indenture providing for a guarantee of payment of the
Securities on the terms provided herein;


<PAGE>

                  WHEREAS, the Boards of Directors of the Issuer, the Guarantor
and the Subsidiary Guarantor have authorized the execution of the Second
Supplemental Indenture and its delivery to the Trustee;

                  WHEREAS, the Company and the Guarantor have delivered an
Opinion of Counsel to the Trustee pursuant to Section 9.03 of the Indenture;

                  WHEREAS, all other actions necessary to make this Second
Supplemental Indenture a legal, valid and binding obligation of the parties
hereto in accordance with its terms and the terms of the Indenture have been
performed; and

                  WHEREAS, the Issuer, the Guarantor, the Subsidiary Guarantor
and the Trustee desire to enter into, execute and deliver this Second
Supplemental Indenture in compliance with the provisions of the Indenture.

                  NOW, THEREFORE, the Issuer, the Guarantor and the Trustee
hereby agree as follows for the benefit of each other and for the equal and
ratable benefit of the Holders of the Notes:

                                   Article I
                              SUBSIDIARY GUARANTEE

                  SECTION 1.01. Guarantee. Subject to the provisions of this
Article One, the Subsidiary Guarantor hereby fully, unconditionally and
irrevocably guarantees to each Holder and to the Trustee on behalf of the
Holders: (i) the due and punctual payment of the principal of, premium, if any,
on and interest (including Special Interest) on each Security, when and as the
same shall become due and payable, whether at maturity, by acceleration or
otherwise, the due and punctual payment of interest on the overdue principal of
and interest, if any, on the Securities, to the extent lawful, and the due and
punctual performance of all other obligations of the Issuer to the Holders or
the Trustee, all in accordance with the terms of such Security and this
Indenture and (ii) in the case of any extension of time of payment or renewal of
any Securities or any of such other obligations, that the same will be promptly
paid in full when due or performed in accordance with the terms of the extension
or renewal, at Stated Maturity, by acceleration or otherwise. The Subsidiary
Guarantor hereby waives diligence, presentment, demand of payment, filing of
claims with a court in the event of merger or bankruptcy of the Issuer, any
right to require a proceeding first against the Issuer, the benefit of
discussion, protest or notice with respect to any such Security or the debt
evidenced thereby and all demands whatsoever, and covenants that this Guarantee
will not be discharged as to any such Security except by payment in full of the
principal thereof and interest thereon and as provided in Section 12.01 and
Section 12.02 (subject to Section 12.06) of the Indenture. The maturity of the
obligations guaranteed hereby may be accelerated as provided in Article Five of
the Indenture for the purposes of this Article One. In the

                                       2

<PAGE>

event of any declaration of acceleration of such obligations as provided in
Article Five of the Indenture, such obligations (whether or not due and payable)
shall forthwith become due and payable by the Subsidiary Guarantor for the
purpose of this Article One. In addition, without limiting the foregoing
provisions, upon the effectiveness of an acceleration under Article Five of the
Indenture, the Trustee shall promptly make a demand for payment on the
Securities under the Guarantee provided for in this Article One.

                  If the Trustee or the Holder of any Security is required by
any court or otherwise to return to the Issuer or the Subsidiary Guarantor, or
any custodian, receiver, liquidator, trustee, sequestrator or other similar
official acting in relation to the Issuer, the Guarantor or the Subsidiary
Guarantor, any amount paid to the Trustee or such Holder in respect of a
Security, this Guarantee, to the extent theretofore discharged, shall be
reinstated in full force and effect. The Subsidiary Guarantor further agrees, to
the fullest extent that the Subsidiary Guarantor may lawfully do so, that, as
between the Subsidiary Guarantor, on the one hand, and the Holders and the
Trustee, on the other hand, the maturity of the obligations guaranteed hereby
may be accelerated as provided in Article Five of the Indenture for the purposes
of this Guarantee, notwithstanding any stay, injunction or other prohibition
extant under any applicable bankruptcy law preventing such acceleration in
respect of the obligations guaranteed hereby.

                  Until such time as the Securities are fully and finally paid,
including all interest, premium, principal and liquidated damages with respect
thereto, the Subsidiary Guarantor hereby irrevocably waives any claim or other
rights which they may now or hereafter acquire against the Issuer that arise
from the existence, payment, performance or enforcement of their obligations
under this Guarantee and this Indenture, including, without limitation, any
right of subrogation, reimbursement, exoneration, contribution, indemnification,
any right to participate in any claim or remedy of the Holders against the
Issuer or any collateral which any such Holder or the Trustee on behalf of such
Holder hereafter acquires, whether or not such claim, remedy or right arises in
equity, or under contract, statute or common law, including, without limitation,
the right to take or receive from the Issuer, directly or indirectly, in cash or
other property or by setoff or in any other manner, payment or Security on
account of such claim or other rights. If any amount shall be paid to the
Subsidiary Guarantor in violation of the preceding sentence and the principal
of, premium, if any, and accrued interest on the Securities shall not have been
paid in full, such amount shall be deemed to have been paid to the Subsidiary
Guarantor for the benefit of, and held in trust for the benefit of, the Holders,
and shall forthwith be paid to the Trustee for the benefit of the Holders to be
credited and applied upon the principal of, premium, if any, and accrued
interest on the Securities. The Subsidiary Guarantor acknowledges that the
Subsidiary Guarantor has received and will receive direct and indirect benefits
from the issuance of the Securities pursuant to the Indenture and that the
waivers set forth in this Section 1.01 are knowingly made in contemplation of
such benefits.

                                       3

<PAGE>

                  The Guarantee set forth in this Section 1.01 shall not be or
become valid or obligatory for any purpose with respect to a Security unless the
certificate of authentication on such Security shall have been signed by or on
behalf of the Trustee.

                  SECTION 1.02. Obligations Unconditional. Subject to Section
1.05, nothing contained in this Article One or elsewhere in the Indenture or in
the Securities is intended to or shall impair, as among the Subsidiary Guarantor
and the holders of the Securities, the obligation of the Subsidiary Guarantor,
which is absolute and unconditional, upon failure by the Issuer, to pay to the
holders of the Securities the principal of, premium, if any, and interest on the
Securities as and when the same shall become due and payable in accordance with
their terms, or is intended to or shall affect the relative rights of the
holders of the Securities and creditors of the Subsidiary Guarantor, nor shall
anything herein or therein prevent the holder of any Securities or the Trustee
on their behalf from exercising all remedies otherwise permitted by applicable
law upon default under this Indenture.

                  Without limiting the foregoing, nothing contained in this
Article One will restrict the right of the Trustee or the holders of the
Securities to take any action to declare the Guarantee to be due and payable
prior to the Stated Maturity of the Securities pursuant to Section 5.02 of the
Indenture or to pursue any rights or remedies hereunder.

                  SECTION 1.03. Notice to Trustee. The Subsidiary Guarantor
shall give prompt written notice to the Trustee of any fact known to the
Subsidiary Guarantor which would prohibit the making of any payment to or by the
Trustee in respect of the Guarantee pursuant to the provisions of this Article
One.

                  SECTION 1.05. Release of the Subsidiary Guarantor. The
Subsidiary Guarantor shall be automatically and unconditionally released and
discharged from its obligations under this Guarantee (i) upon any sale, exchange
or transfer, to any Person not an Affiliate of the Guarantor, of all of the
Guarantor's and each Restricted Subsidiary's Capital Stock in, or all or
substantially all the assets of, the Subsidiary Guarantor (which sale, exchange
or transfer is not prohibited by the Indenture) or (ii) at any time, so long as
in the case of this clause (ii) Standard & Poor's Corporation, or any successor,
is notified by the Issuer of the proposed termination of the Guarantee of the
Subsidiary Guarantor and advises the Issuer that such termination would not
result in a downgrade of the rating on the Securities or placement of the
Securities on creditwatch with negative implications.

                                       5

<PAGE>

                                   Article II
                                  MISCELLANEOUS

                  SECTION 2.01. Trustee's Disclaimer. The Trustee shall not be
responsible for and makes no representation as to the validity or adequacy of
this Second Supplemental Indenture or the Securities, and it shall not be
responsible for any statement of the Issuer or the Guarantor or the Subsidiary
Guarantor in this Second Supplemental Indenture.

                  SECTION 2.02. Ratification. Except as hereby expressly
amended, the Indenture and the Securities issued thereunder are in all respects
ratified and confirmed and all the terms, conditions and provisions thereof
shall remain in full force and effect. Upon execution, this Second Supplemental
Indenture shall form a part of the Indenture and the Second Supplemental
Indenture and the Indenture shall be read, taken and construed as one and the
same instrument for all purposes, and every holder of Securities heretofore or
hereafter authenticated and delivered under the Indenture shall be bound hereby.

                  SECTION 2.03. Effectiveness. This Second Supplemental
Indenture shall become effective as of the date first above written.

                  SECTION 2.05. Governing Law. THIS SECOND SUPPLEMENTAL
INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF NEW YORK, AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE
OF NEW YORK, WITHOUT REGARD TO PRINCIPLES OF CONFLICT OF LAWS.

                  SECTION 2.05. Counterpart Originals. The parties may sign any
number of copies of this Second Supplemental Indenture. Each signed copy shall
be an original, but all of them together represent the same agreement. One
signed copy is enough to prove this Second Supplemental Indenture.

                                       5

<PAGE>
                                   SIGNATURES

                  IN WITNESS WHEREOF, the parties hereto have caused this Second
Supplemental Indenture to be duly executed, and their respective corporate seals
to be hereunto affixed and duly attested, all as of the day and year first above
written.

The Company Seal of RSL COMMUNICATIONS PLC
was hereto affixed in the presence of:



[Seal]


                                             RSL COMMUNICATIONS PLC,



                                             By: /s/ Donald R. Shassian
                                                 ------------------------------
                                                 Name:
                                                 Title:



                                             By: /s/ Margaret B. Niche
                                                 ------------------------------
                                                 Name:
                                                 Title:


                                             THE CHASE MANHATTAN BANK



                                             By: /s/ Robert S. Peschler
                                                 ------------------------------
                                                 Name:  Robert S. Peschler
                                                 Title: Assistant Vice President


                                             RSL COMMUNICATIONS, LTD.,



                                             By: /s/ Donald R. Shassian
                                                 ------------------------------
                                                 Name:
                                                 Title:


<PAGE>

                                             RSL COM U.S.A., INC.



                                             By: /s/ Joel Beckoff
                                                 ------------------------------
                                                 Name:
                                                 Title: