<PAGE>   1
                                                                    Exhibit 10.6
                             [FLASHCOM LETTERHEAD]

November 16, 1999


Richard N. Rasmus
9 Westview Road
Bryn Mawr, PA 19010


Dear Richard:

        We are pleased to offer you a position with Flashcom, Inc. (the
"Company") as its President and Chief Operating Officer, commencing as soon as
possible. Immediately following the closing of the Series B financing, you will
assume the title and role of President and CEO. Prior to and following the
Series B financing, you will be an officer of the company and a board member,
and you will report directly to the Board of Directors. Your primary
responsibilities will be to lead the Company's business, including: sales,
marketing, operations and other areas of the business. The other executive
officers of the Company, including Chris Rose, the acting Chief Financial
Officer, will report directly to you. You will be expected to perform your
principal service to the Company in Orange County, California.

        You will receive salary at the rate of $200,000 per year, which will be
paid in accordance with the Company's normal payroll procedures. You will also
be entitled to a $75,000 interest-free loan payable to you after 30 days of
employment. If you voluntarily terminate your employment other than for good
reason (as hereinafter defined) within one year of the receipt of such loan, the
loan will be due and payable to the Company within 30 days of your termination
date. This loan will be forgiven upon the earlier to occur of (i) one year
following the date of receipt, or (ii) at such time as the Company should
terminate your employment without cause or you shall terminate your employment
with good reason. As used herein, the term "good reason" shall mean (x) your
assignment to duties inconsistent in any material respect with the duties set
forth in the first paragraph of this letter (it being agreed that employment as
the Company's President and Chief Operating Officer shall not be inconsistent
with such duties), (y) any failure by the Company to provide you with the
compensation and benefits set forth in this letter (other than failures not made
in bad faith and which are remedied by the Company within five (5) business days
after notice thereof) or (z) any failure by the Company to require any successor
entity to expressly assume and agree to perform the terms of this agreement.

        In addition, you will be eligible to receive a bonus of $100,000 during
the first year of your employment with the Company. Such bonus shall be paid in
four quarterly installments on the last day of each quarter beginning with the
quarter ending March 31, 2000 based upon achievement of milestones to be agreed
upon by you and the Board of Directors prior to the beginning of each such
quarter, provided that the first quarterly bonus shall be guaranteed. The
Company will reimburse you for up to $150,000 in moving expenses, commuting
expenses to and from Pennsylvania, legal expenses incurred in connection with
the negotiation and signing of this agreement and family travel in connection
with house-hunting, in each case based on receipts dated no later than twelve
(12) months after the date of this letter. As a Company employee, you will also
be eligible to receive the

<PAGE>   2
Mr. Richard Rasmus
November 11, 1999
Page 2 of 4



medical insurance and other employee benefits generally available from time to
time to the highest tier of employees of the Company.

        Further, in connection with your purchase of a home in Southern
California, the Company will extend to you a loan, secured by a second lien on
the home you purchase, for up to $250,000 at the minimum federal interest rate
applicable at the time of your purchase, or if not permissible by the lender, by
other collateral acceptable to you, the Company and the lender. The loan must be
repaid upon the first to occur of (i) 60 days following the closing of the sale
by you of your home in Bryn Mawr, PA, (ii) 60 days following a liquidity event
of the Company whereby you receive cash proceeds of at least $250,000 (including
an initial public offering of our common stock or the sale of substantially all
of our stock or assets), (iii) twelve months following termination of your
employment by the Company without cause or by you for good reason, or (iv) six
months following any other termination of your employment with the Company. In
addition, the Company agrees to pay reasonable expenses, based on receipts which
you provide to the Company, of up to $3,000 per month toward the rent on your
house in Southern California or, if you purchase a house in California, the debt
service on the mortgage, until the earlier to occur of (a) the twelfth monthly
installment made under such arrangement (with aggregate payments not to exceed
$36,000), or (b) the sale of your house in Bryn Mawr, PA.

        Also in connection with your employment, the Company will grant you an
option to purchase shares of Common Stock equal to five percent (5%) of the
Company's currently outstanding shares of Common Stock (including shares
issuable to you) on an as-converted and fully diluted basis, or 880,481 shares
(based on 9,245,312 shares of Common Stock, 5,771,679 shares of Series A
Preferred Stock and 1,888,157 options and warrants currently outstanding). Your
option shall be issued at an exercise price per share equal to the fair market
value of the Common Stock (which shall not exceed the initial conversion price
of the Series B Preferred Stock sold in our currently contemplated financing) as
determined by the Board at its first meeting following the start of your
employment with the Company, and pursuant to the terms and conditions contained
in the Company's standard form of stock option agreement in substantially the
form enclosed for your reference, which provides for, among other things,
vesting of 25% after one year of employment and additional vesting of 25% upon
each additional year of employment. Such option shall, to the maximum extent
allowable by law, constitute an incentive stock option, and the remaining
portion of such option shall constitute a nonqualified stock option. The Company
will offer you the option of paying the exercise price for your option by any of
the methods set forth in Section 5.3 of the Company's option plan, to the extent
permitted by applicable laws.

        Your employment will commence promptly after you have served any
required notice period with your current employer, but in any event within 31
days following execution of this Agreement. You should be aware that your
employment with the Company is for no specified period and constitutes "at-will"
employment. As a result, you are free to resign at any time, for any reason or
for no reason. Similarly, the Company is free to conclude its employment
relationship with you at any time, with or without cause. However, if the
Company elects to terminate its employment relationship with you without cause,
or if you terminate your employment for good reason, you and the Company agree
that you will sign a standard form of settlement agreement stating the terms
below and a general release, and in consideration therefor, the Company will
provide you a settlement of (i) acceleration of vesting of the exercisability of
the option to be granted to you equal to the greater of (A) twelve (12) months
of additional vesting or (B) vesting through the first year

<PAGE>   3
Mr. Richard Rasmus
November 11, 1999
Page 3 of 4



cliff of your vesting schedule, and (ii) twelve (12) months' salary plus
$50,000. With respect to the shares that are to vest or cash that is to be paid
to you pursuant to this paragraph, one-twelfth of such shares or cash shall vest
or be paid to you, as the case may be, monthly, in each case subject to your
compliance with the terms of the settlement agreement.

        You have provided the Company with copies of all agreements you have in
connection with your employment by Comcast (the "Employment Agreements"), which
include a covenant not to compete and certain prohibitions against using
confidential information. You represent to the Company that (i) you have
provided to the Company complete and accurate copies of all agreements you have
in connection with your employment by Comcast (via a memo to Todd Brooks, David
Helfrich, Brad Sachs and Connie Adair dated September 11, 1999 and a Comcast
employment offer letter faxed to the Company's legal counsel by your attorney,
Ivan Dreyer, on November 11, 1999), and that the Employment Agreements set forth
your entire agreement with Comcast material to our evaluation of your
obligations under the Employment Agreements, (ii) that you have, or by the time
your employment with Comcast terminates, will have, returned all written
materials of Comcast that may contain confidential or other proprietary
information of Comcast and (iii) that you will not bring, use, provide or show
any confidential or other proprietary information of Comcast to or for the
benefit of the Company. In reliance on the truth and accuracy of your
representations, the Company agrees to protect and indemnify you from any cost,
damages and liabilities that you may become subjected to were Comcast to
commence any action, suit or other proceeding against you arising out of or in
connection with the termination of your employment or alleging a violation or
breach of your Employment Agreement (any such action, suit or proceeding
including any counterclaim asserted therein being referred to as a
"Proceeding"). The Company hereby acknowledges that the Executive would not
relocate and accept employment with the Company without the foregoing
indemnities. The Company hereby agrees to indemnify you and hold you harmless
from and against any and all expenses (including the fees and expenses of
attorneys and other advisors), court costs, cost of investigation, cost of
travel, losses, liabilities, claims, damages, judgments and fines (collectively,
"Damages") awarded against you or paid in any settlement consented to by the
Company arising out of or in connection with any Proceeding. You shall give the
Company prompt notice of any such Proceeding, shall contest or prosecute, as
applicable, any such Proceeding, with counsel selected by the Company and
reasonably acceptable to you, and shall keep the Company informed with respect
to the status thereof unless the representation of you by the Company's counsel
would be inappropriate due to conflicting interests, in which event you may
employ counsel of your choice in such defense and the Company will advance the
reasonable fees and expenses of such counsel as it would have had you engaged
counsel selected by the Company. You agree, however, that you shall not enter
into any settlement without the consent of the Company, which consent shall not
be unreasonably withheld or delayed.

        In addition, if in connection with any Proceeding you are enjoined from
continuing to work for the Company, the Company will continue to pay your base
salary only for a period until you find other employment (not to exceed twelve
(12) months); provided that during such period you agree to use your reasonable
best efforts to secure a comparable position with another employer. If you are
enjoined, unless we otherwise agree, you will be deemed to have voluntarily
terminated your employment as of the date of the injunction (except that in such
case, the $75,000 loan need only be repaid within 90 days) and the Company's
sole obligation to you hereunder shall be to pay you your

<PAGE>   4
Mr. Richard Rasmus
November 11, 1999
Page 4 of 4



base salary as provided in the preceding sentence and to indemnify you as
provided in the preceding paragraph.

        For purposes of federal immigration law, you will be required to provide
to the Company documentary evidence of your identity and eligibility for
employment in the United States. Such documentation must be provided to us
within three (3) business days of your date of hire, or our employment
relationship with you may be terminated.

        I have enclosed our standard Proprietary Information Agreement. If you
accept this offer, please return to me a signed copy of that agreement.

        In the event of any dispute or claim relating to or arising out of our
employment relationship, you and the Company agree that all such disputes shall
be fully and finally resolved by binding arbitration conducted by the American
Arbitration Association in Orange County, California. HOWEVER, we agree that
this arbitration provision shall not apply to any disputes or claims relating to
or arising out of our indemnity obligations hereunder or the misuse or
misappropriation of the Company's trade secrets or proprietary information.

        To indicate your acceptance of the Company's offer, please sign and date
this letter in the space provided below and return it to me. A duplicate
original is enclosed for your records. This letter, along with the agreement
relating to proprietary rights between you and the Company, set forth the terms
of your employment with the Company and supersede any prior representations or
agreements, whether written or oral. This letter may not be modified or amended
except by a written agreement, signed by the Company and by you.

        We look forward to your joining the Flashcom team! Please acknowledge
your acceptance of this offer by returning a signed copy of this offer letter to
us by November 18, 1999. This offer expires on November 18, 1999.

        If you have any questions about the contents of this letter, or
employment at the Company, please feel free to contact Todd Brooks or Brad
Sachs.

FLASHCOM, INC.



/s/ Brad Sachs                              /s/ Todd A. Brooks
-------------------------------------       ------------------------------------
Brad Sachs                                  Todd A. Brooks
Chief Executive Officer & Chairman          Director





AGREED TO AND ACCEPTED this
16th day of November, 1999.



/s/ Richard N. Rasmus
------------------------------------
Richard N. Rasmus

Enclosures:    Duplicate Original Letter
               Form of Stock Option Agreement
               Proprietary Information Agreement