<PAGE>   1
                                                                   EXHIBIT 10.20



                        ASSIGNMENT OF ACCOUNTS RECEIVABLE

          The undersigned, Let's Talk Cellular & Wireless, Inc., a Florida
 corporation ("Assignor"), in consideration of the sum of $1,960,571.00 from
 H.I.G. Capital LLC ("Assignee"), the receipt and sufficiency of which are
 hereby acknowledged, hereby sells, assigns, transfers and conveys absolutely
 and not as collateral to Assignee all of its right, title and interest, in and
 to the accounts receivable owed to the Assignor by the account debtors listed
 on SCHEDULE A (each, a "Debtor"), which are particularly described on the
 schedule attached hereto as SCHEDULE "A" (the "Receivables"). Notwithstanding
 anything to the contrary set forth in the prior sentence, the Receivable does
 not include amounts owing from the Debtor other than as speci ically described
 on the Schedule attached hereto as SCHEDULE "A."

          Assignor represents that (1) the Receivables have an outstanding
 balance of $2,000,582.00 that Assignor is owed by the Debtor, (ii) all
 amounts received by Assignor with respect to the Receivables hereby assigned
 have been credited and deducted in determining the amount of the Receivables,
 and (iii) Assignee shall have all rights Assignor has with respect to the
 Receivables including without limitation, the right to enforce, collect,
 compromise or settle the Receivables, and the right to put the Debtor on notice
 of the assignment of the Receivables.

          Assignor hereby unconditionally guarantees payment of the amount of
 the Receivables to Assignee in accordance with the terms set forth on Exhibit
 "A." Assignor further agrees to indemnify Assignee for any amounts which
 Assignee may be required to pay relating to the Receivables, including but not
 limited to any amounts which Assignee may be required to disgorge pursuant to
 Section 544(a) or 547(a) of the Bankruptcy Code, or otherwise. For the purposes
 hereof, any payment required to be made by Assignor to Assignee pursuant to the
 two (2) foregoing sentences shall be referred to herein as a "Distribution".
 Assignor agrees that Assignee shall have no liability for any counterreceivable
 or right of setoff, recoupment the



<PAGE>   2




 like. Assignee agrees that any Distribution required to be paid is and shall be
 expressly junior and subordinated in right of payment to all amounts due and
 owing upon all Senior Indebtedness (as hereafter defined) outstanding from time
 to time. "Senior Indebtedness" shall mean all Obligations of any kind owed by
 Assignor or its subsidiaries to The Chase Manhattan Bank, as agent ("Agent"),
 and the lenders ("Lenders") who are parties to, the Loan and Security Agreement
 dated as of April 2, 1998 between Assignor, its subsidiaries, Agent and the
 Lenders (as same has been amended from time to time, the "Credit Agreement")
 under or pursuant to the Credit Agreement including, without limitation, all
 principal, interest (including all interest accruing after commencement of any
 case, proceeding or other action relating to the bankruptcy, insolvency or
 reorganization of Assignor or its subsidiaries) accruing thereon, charges,
 expenses, fees and other sums chargeable to Assignor or its subsidiaries by
 Agent or Lenders and reimbursement, indemnity or other obligations due and
 payable Agent or Lenders. Senior Indebtedness shall continue to constitute
 Senior Indebtedness, notwithstanding the fact that such Senior Indebtedness or
 any claim for such Senior Indebtedness is subordinated, avoided or disallowed
 under the federal Bankruptcy Code or other applicable law. Specifically, but
 not by way of limitation:

                   (a) PAYMENT. Assignor shall make no Distribution until such
 time as the Senior Indebtedness shall have been paid in full in cash and the
 Credit Agreement shall have been irrevocably terminated; PROVIDED, HOWEVER, so
 long as (i) no Default or Event of Default shall have occurred under the Credit
 Agreement and (ii) Borrowers shall have Undrawn Availability of at least
 $1,000,000 after giving effect to the payment of such Distribution, Assignor
 may pay and Assignee may receive Distributions.

          Following the occurrence of a Default or an Event of Default under the
 Credit Agreement or, if Undrawn Availability would be less than $1,000,000
 after giving effect



                                       -2-


<PAGE>   3




 to any Distribution, (i) Assignor shall make no Distribution and (ii) Assignee
 shall not be entitled to receive or retain any such Distribution, PROVIDED,
 FURTHER, that notwithstanding the foregoing restriction, Assignor may pay and
 Assignee shall be entitled to receive and retain any Distribution which shall
 have become due and payable on the earliest to occur of (x) the date on which
 (i) all such Defaults and/or Events of Default shall have been cured or waived
 and (ii) Undrawn Availability shall equal or exceed $1,000,000 after giving
 effect to such Distribution or (y) payment in full in cash of all Senior
 Indebtedness and the irrevocable termination of the Credit Agreement.

                   (b) LIMITATION ON ACCELERATION. During any period described
 above in which a Distribution is not permitted to be made (any such period, a
 "Non-Payment Period"), Assignee shall not be entitled to exercise any remedies
 or commence any action or proceeding to recover any amounts due or to become
 due with respect to any Distribution, PROVIDED, HOWEVER, the foregoing
 limitation on acceleration or exercise of any remedies shall not be applicable
 following (x) the occurrence of an Event as defined below or (y) following the
 maturity or acceleration of all Senior Indebtedness.

                   (c) PRIOR PAYMENT OF SENIOR INDEBTEDNESS IN BANKRUPTCY, ETC.
 In the event of any insolvency or bankruptcy proceedings relative to Assignor,
 its subsidiaries or their property, or any receivership, liquidation,
 reorganization or other similar proceedings in connection therewith, or, in the
 event of any proceedings for voluntary liquidation, dissolution or other
 winding up of Assignor or its subsidiaries or distribution or marshalling of
 their assets or any composition with creditors of Assignor or its subsidiaries,
 whether or not involving insolvency or bankruptcy, or if Assignor or its
 subsidiaries shall cease their operations, call a meeting of their creditors or
 no longer do business as a going concern (each individually or collectively, an
 "Event") then all Senior Indebtedness shall be paid in full and satisfied in
 cash and the Credit


                                       -3-


<PAGE>   4




 Agreement irrevocably terminated before any Distribution shall be made. Any
 such Distribution which would, but for the provisions hereof, be payable or
 deliverable, shall be paid or delivered directly to the Agent or its
 representatives, in the proportions in which they hold the same, until amounts
 owing upon Senior Indebtedness shall have been paid in full in cash and the
 Credit Agreement has been irrevocably terminated.

                   (d) ACCELERATION. In the event of any Senior Indebtedness
 becoming due and payable, whether by acceleration, maturity or otherwise, no
 Distribution shall thereafter be made until all Senior Indebtedness shall be
 paid in full in cash and the Credit Agreement irrevocably terminated.

                   (e) PAYMENTS HELD IN TRUST. Should any Distribution be
 collected or received by Assignee or any Affiliate (as such term is defined in
 rule 405 of Regulation C adopted by the Securities and Exchange Commission
 pursuant to the Securities Act of 1933) of Assignee at a time when the
 Assignee is not permitted to receive any such Distribution or proceeds thereof
 including if same is collected or received when there is or would be after
 giving effect to such payment a Default or an Event of Default under the Credit
 Agreement, then the Assignee will forthwith deliver, or cause to be delivered,
 the same to the Agent in precisely the form held by the Assignee (except for
 any necessary endorsement) and until so delivered, the same shall be held in
 trust by the Assignee, or any such Affiliate, as the property of the Agent and
 shall not be commingled with other property of the Assignee or any such
 Affiliate.

          Notwithstanding the foregoing, in the event that Assignee shall not
 receive payment of all or any part of the Receivables within ninety (90) days
 of the date of this Agreement or the Assignee shall have reasonably determined
 that the Receivable will not be paid by the account debtor due to the financial
 inability of the account debtor to pay such Receivable (any such sum, the
 "Unpaid Amount"), Assignee shall have the right to acquire additional
 Receivables from

                                       -4-


<PAGE>   5




 Assignor with the same representations and warranties contained in paragraph 2
 hereof in an amount equal to such Unpaid Amount up to an aggregate sum of
 $300,000; provided, the additional Receivables transferred to Assignee (x) are
 due and unpaid more than ninety (90) days past the original invoice date
 therefor and (y) do not have an aggregate outstanding balance in excess of the
 lesser of (x) $300,000 or (y) the Unpaid Amount.

          Assignor shall provide assistance as follows in connection with the
 assignment of the Receivables:

          A. Reasonable documentation to support the Receivables;

          B. Knowledgeable witnesses to offer testimony on the validity of the
 Receivables, including without limitation, testimony as to the basis for the
 Receivables, if necessary.

          C. Such other information and help as Assignee reasonably requests.

          D. Provision of written notice to Debtor of assignment of the
Receivables to Assignee.

          This Assignment shall be governed by the laws of the State of
New York.

          June __, 1999

                                       Assignor

                                       LET'S TALK CELLULAR & WIRELESS, INC.


                                       By: /s/ Daniel Cammarata
                                          ---------------------------------
                                          Name: Daniel Cammarata
                                          Title: Chief Financial Officer

                                       Assignee

                                       H.I.G. CAPITAL LLC


                                       By: /s/ Douglas Berman
                                          ---------------------------------
                                          Name: Douglas Berman
                                          Title: Managing Director




                                       -5-

<PAGE>   6




                                   SCHEDULE A



          Lets Talk Cellular & Wireless
          Detail of Receivables
          As of 4/30/99
<TABLE>
<CAPTION>

                                                                                                    Detail of
                                                                                              Receivables for
          System      Vendor Code                 Carrier                                  ll/l/98 - 01/30/99
          ---------------------------------------------------------------------------------------------------
<S>                   <C>                         <C>                                              <C>
          Prism       AIRTROUCH                   Airtouch                                         104,584.05
          Prism       ATTCO                       AT&T Colorado                                     56,645.02
          Prism       ATT-LA                      AT&T Calif.                                       50,395.01
          Prism       ATTPCS                      AT&T DC                                           87,360.01
          Prism       ATTPCSNATL                  AT&T PCS National                                (11,585.09)
          Prism       BAPHILLY                    Bell Atlantic - Philly                            80,720.03
          Prism       BS                          Bell South - So Fla.                              68,798.08
          Prism       BS03                        Bell South - Orlando                              10,365.66
          Prism       CELLONENY                   Cellular One - New York                           27,073.78
          Prism       COMCAST                     Comcast Cellular Communication                    12,504.00
          Prism       GTESANFRAN                  GTE San Francisco                                392,782.31
          Prism       LACELLULAR                  AT&T (AKA L.A. Cellular)                          83,209.96
          Prism       LVATT                       AT&T Las Vegas                                    69,805.01
          Prism       OMNIPOINT                   Omnipoint Communications                          39,989.00
          Prism       SNET                        SNET of Connecticut                              129,974.96
          Prism       SPRINT                      Sprint Spectrum LP                                 2,939.51
          Prism       TAMPAGTE                    GTE Mobilenet - Tampa                              9,128.98
          GERS        1 AIRDETROIT                Airtouch Cellular DT                              30,060.00
          GERS        2 T-ATTl                    AT&T Wireless Activations                        343,295.00
          GERS        2 T-CEL1                    Cellular One Kansas Activations                   36,700.00
          GERS        2 V-ATTAUSTI                AT&T Wireless Austin                              15,765.00
          GERS        1 V-ATTPCNAT                AT&T PCS National                                 19,650.00
          GERS        1 V-CELL1 BUF               Cellular One Buffalo                              39,062.75
          GERS        I V-CELL1 CH                Cellular One Chicago                             273,950.00
          GERS        1 V-CELL1 ROC               Cellular One Rochester                          (111,742.04)
          GERS        1 V-CELL1 SYR               Cellular One Syracuse                             72,058.00
          GERS        1 V-GTEINDIA                GTE Indianapolis                                  67,094.00
          ---------------------------------------------------------------------------------------------------
                                                  Grand Totals                                   2,000,582.99
</TABLE>







 LET'S TALK CELLULAR CONFIDENTIAL                                      Page 1