The error message is quite explicit:
System.IO.FileNotFoundException: Could not load file or assembly 'GSMCommShared, Version=1.21.0.0, Culture=neutral, PublicKeyToken=515d87df384dcc81' or one of its dependencies. The system cannot find the file specified.
It would appear that you have not included the DLL in your server installation.
I assume you realize that this will only work if the phone is plugged into the server, not the client? Because you'd be surprised how many people don't think about that...