<PAGE>
                                                                   EXHIBIT 10.90

    Shareholder's Voting Rights Proxy Agreement-Participation Letter of Shenzhen
                                                                         Bianjie

                   ACKNOWLEDGEMENT LETTER FOR PARTICIPATION OF

                   SHAREHOLDERS' VOTING RIGHTS PROXY AGREEMENT

SHANGHAI FOCUS MEDIA ADVERTISEMENT CO., LTD., (registered address: Room 1003 F,
No.1027, Changning Road, Changning District, Shanghai) and SHANGHAI FOCUS MEDIA
ADVERTISING AGENCY CO., LTD., (registered address: Room A65, 28 Floor,
No.369, Jiangsu Road, Changning District, Shanghai) (hereinafter the
"PARTICIPATING SHAREHOLDER"), and SHENZHEN BIANJIE BUILDING ADVERTISEMENT CO.,
LTD. (registered address: Room 1020A, Qunxing Plaza, No. 38 Hongli Road, Futian
District, Shenzhen) (hereinafter the "PARTICIPATED TARGET COMPANY"), as
independent party, hereby agree to participate in the Shareholders' Voting
Rights Proxy Agreement among Focus Media Technology (Shanghai) Co., Ltd.
(hereinafter "FOCUS MEDIA TECHNOLOGY"), Shanghai Focus Media Advertisement Co.,
Ltd. and other relevant parties (hereinafter the "PROXY AGREEMENT") dated March
28 2005. Participating Shareholder and Participated Target Company agree to
entrust the Trustees designated by Focus Media Technology to exercise the voting
rights in Participated Target Company in respect of 100% of the equity interest
in the registered capital of Participated Target Company held by the
Participating Shareholder as of the date of this Acknowledgement Letter, on
behalf of Participating Shareholder.

Once this Acknowledgement Letter is executed by the Participating Shareholder
and Participated Target Company, Participating Shareholder and Participated
Target Company shall be deemed to have made the same undertakings and warranties
with those of the Shareholders and Target Companies under the Proxy Agreement
(to the extent that is related and applicable to Participating Shareholder and
Participated Target Company), agreed to respectively perform the obligations of
the Shareholders and Target Companies stipulated in the Proxy Agreement (to the
extent that is related and applicable to Participating Shareholder and
Participated Target Company), and

<PAGE>

    Shareholder's Voting Rights Proxy Agreement-Participation Letter of Shenzhen
                                                                         Bianjie

acknowledged the rights and obligations of the Parties under the Proxy
Agreement.

                                [EXECUTION PAGE]

SHANGHAI FOCUS MEDIA ADVERISEMENT CO., LTD.
(Company chop)

Signature by: /s/ Jason Nanchun Jiang
              ------------------------------
Name: Jason Nanchun Jiang
Position: Authorized Representative
Date: May 22, 2006

SHANGHAI FOCUS MEDIA ADVERTISING AGENCY CO., LTD.
(Company chop)

Signature by: /s/ Jason Nanchun Jiang
              ------------------------------
Name: Jason Nanchun Jiang
Position: Authorized Representative
Date: May 22, 2006

SHENZHEN BIANJIE BUILDING ADVERTISEMENT CO., LTD.
(Company chop)

Signature by: /s/ Jason Nanchun Jiang
              ------------------------------
Name: Jason Nanchun Jiang
Position: Authorized Representative
Date: May 22, 2006

FOCUS MEDIA TECHNOLOGY (SHANGHAI) CO., LTD.
(Company chop)

Signature by: /s/ Jason Nanchun Jiang
              ------------------------------
Name: Jason Nanchun Jiang
Position: Authorized Representative
Date: May 22, 2006