By the time you read this, Null Team and Legba will have released YateBTS 2.0. The big new features are authentication and USSD, both of which are important stepping stones for roaming support, and a new web-based interface for network-in-a-PC configuration (NiPC). (Note that USSD support is in the commercial release only.)
Meanwhile at Legba, we are working on other aspects of YateBTS, like EDGE, for upcoming releases.
More on that soon.