TpSession library provides simplified layer top of Telepathy with easy to use API. TpSession is not abstraction layer that tries to hide Telepathy-Qt4 API, it just provides simple methods to perform most common use cases. At the moment, TpSession is early proof of concept and it is missing lot of features. Current version only supports textual SMS and IM with any of Telepathy connection Managers. When TpSession is not abstratction layer, it is not cross platform for non telepathy environments. Qt Mobility will be cross platform abstraction layer and TpSession is used as adaptation layer for Fremantle Qt Mobility.
By default, you should use QtMobility always when it provides functions you need.QtMobility is cross platform, TpSession works only in Maemo or it may work other plaforms using Telepathy Framework. If you need some functionality not provided by QtMobility, you can use TpSession. With Maemo Fremantle QtMobility you can access TpSession features with TpSession::getinstance()
libtpsession is available from maemo fremantle extras-devel repository. Due limitations of the build system, I can't upload latestfixed version to extras-devel, tae it from git or repository.katix.org