You may encounter following link errors when building sipXtapi:

\sipXtapi-media-update\Speex\lib\libspeex.lib : fatal error LNK1262: link failed due to mismatched versions of 'C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\bin\c2.dll' and LINK.EXE

or following :

Linking...
LINK : warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:ICF' specification
libspeex.lib(bits.obj) : warning LNK4218: non-native module found; restarting link with /LTCG
LINK : warning LNK4075: ignoring '/INCREMENTAL' due to '/LTCG' specification
MSVCRT.lib(MSVCR71.dll) : error LNK2005: __strdup already defined in LIBCMTD.lib(strdup.obj)

This is NOT sipXtapi errors. Please, do not send reports to sipXtapi mailing list, report this to Speex-dev list.
This errors come from the point that prebuilt Speex-1.2beta use Visual Studio 2005 static multi-threaded runtime, incompatible with Visual Studio 2003 in general and DLL multi-threaded runtime in particular.

You may use attached vcproj file to build Speex yourself or just use attached prbuilt versions.