UPDATE: Microsoft Fixes Live Mesh Mobile Client
From the Live Mesh blog...
"Thank you for using the Live Mesh for Mobile client! For users who saw a failure to add their mobile phone to their mesh, we have deployed an updated build of Live Mesh for Mobile. You will need to download the Mobile Installer from http://m.mesh.com/install/wm6/LiveMesh.cab again. Once you have the new installer on your phone, run it and the installed client will be upgraded to the new version. The new Mobile Live Mesh Client is version number 0.9.3424.6 (check this through Menu -> About). Now you can start Live Mesh, sign in, and you should be good to go."
Get you client installer OTA: