Mobile21

Mobile21 Co., Ltd. (モバイルニジュウイチ株式会社) was a Japanese video game developer that was a 50/50 joint venture between Nintendo and Konami established on October 7, 1999. Mobile21 primarily concentrated on next-generation Game Boy Advance development, with a particular interest in mobile phone linking features.

On 1999-09-02, Nintendo Corporation and Konami Corporation announced the establishment of Mobile21 Co., Ltd., with the Mobile Adapter GB on sale in April 2000.

The Mobile Adapter GB service began on January 27, 2000, and was terminated on December 14, 2002. However, the wireless feature was later found in Game Boy Advance Wireless Adapter.

...
Wikipedia