SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant x   Filed by a Party other than the Registrant ¨

Check the appropriate box:

¨ Preliminary Proxy Statement

¨ Confidential, for use of the Commission Only (as permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

x  Definitive Additional Materials

¨ Soliciting Material Pursuant to Sec. 240.14a-12.

DWS ADVISOR FUNDS

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment Of Filing Fee (Check the appropriate box):

x  No fee required.

¨ Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

1)  Title of each class of securities to which transaction applies:

2)  Aggregate number of securities to which transaction applies:

3)  Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 0-11 (set forth the amount on which the filing fee is calculated and state how it was determined):

4)  Proposed maximum aggregate value of transaction:

5)  Total fee paid:

¨ Fee paid previously with preliminary materials.

¨ Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the form or schedule and the date of its filing.

1)  Amount Previously Paid:

2)  Form, Schedule or Registration Statement No.:

3)  Filing Party:

4)  Date Filed:

Investors Municipal Cash Fund

Important Proxy

News

PLEASE VOTE TODAY!

Dear Shareholder:

Recently, we distributed proxy materials regarding the Special Meeting of Shareholders of Tax-Exempt New York Money Market Fund of Investors Municipal Cash Fund. This meeting, which was originally scheduled for December 8, 2006, has been adjourned to January 25, 2007 at 4:00 p.m. Eastern time at the offices of Deutsche Asset Management, 345 Park Avenue, New York, NY 10154. To date, our records indicate that we have not received your voting instructions. We are still accepting votes to increase shareholder participation.

After careful consideration, the Board of Trustees recommends that shareholders vote “FOR” the proposal. Your vote is important no matter how many shares you own. We urge you to act promptly in order to allow us to obtain a sufficient number of votes and avoid the cost of additional solicitation.

For your convenience, please utilize any of the following methods to submit your vote:

1. By Phone.

Please call Computershare Fund Services toll-free at 866-774-4940. Representatives are available to take your vote Monday through Friday between the hours of 9:00 a.m. and 11:00 p.m. and Saturday from 12:00 p.m. to 6:00 p.m. Eastern time. Please have your proxy card available.

2. By Internet.

Visit www.vote.proxy-direct.com and follow the simple on-screen instructions.

3. By Touch-Tone Phone.

Dial the toll-free number found on your proxy card and follow the simple instructions.

4. By Mail.

Simply return your executed proxy card in the envelope provided. However, please try to utilize one of the three options above to register your vote, so it may be received in time for the meeting.

WE NEED YOUR HELP. PLEASE VOTE TODAY!

Investors Municipal Cash Fund

Important Proxy

News

PLEASE VOTE TODAY!

Dear Shareholder:

Recently, we distributed proxy materials regarding the Special Meeting of Shareholders of Tax-Exempt New York Money Market Fund of Investors Municipal Cash Fund. This meeting, which was originally scheduled for December 8, 2006, has been adjourned to January 25, 2007 at 4:00 p.m. Eastern time at the offices of Deutsche Asset Management, 345 Park Avenue, New York, NY 10154. To date, our records indicate that we have not received your voting instructions. We are still accepting votes to increase shareholder participation.

After careful consideration, the Board of Trustees recommends that shareholders vote “FOR” the proposal. Your vote is important no matter how many shares you own. We urge you to act promptly in order to allow us to obtain a sufficient number of votes and avoid the cost of additional solicitation.

For your convenience, please utilize any of the following methods to submit your vote:

1. By Internet.

Visit www.proxyvote.com and follow the simple on-screen instructions.

2. By Touch-Tone Phone.

Dial the toll-free number found on your proxy card and follow the simple instructions.

3. By Mail.

Simply return your executed proxy card in the envelope provided. However, please try to utilize one of the above options to register your vote, so it may be received in time for the meeting.

WE NEED YOUR HELP. PLEASE VOTE TODAY!