unity3d 3.0 not support netframework 3.0?

Unity uses .NET 3.5 via Mono 2.6.3

If it's missing anything, it's generally because the default build profile is set to .net 2.0 subset to lower build sizes.

If that is the case, go to Edit > Project Settings > Player, expand other settings in the platform you're interested in and change the Api Compatability Level to .NET 2.0.

The reason that it says 2.0 instead of 3.5 there is that 3.5 is bytecode compatible with 2.0

System.Speech.dll is in netframework3.0,but in unity3 an error display:

NotImplementedException: The requested feature is not implemented. System.Type.GetTypeFromCLSID (Guid clsid) System.Speech.Internal.ObjectTokens.ObjectToken.CreateObjectFromToken[Object] (System.String name)

why implemented? any advice is welcomed

Mono has a lot of the features of .net but some things are yet to be implemented. Given the exception, I would expect this is one of them.

mono develop 2.4 support sapi5.3 while unity3d 3.0 not.That's to say unity3 only support .NET 2.0?