I started to implement Layer-1 support in OsmocomBB for traffic channels. Its not yet ready and in a rather crude state but I hope to clean it up in the next few days so that it can be released.
During testing I used a nice feature of my HP8922 GSM Testset: It can continuously generate Full-Rate TCH speech traffic on a timeslot without the need for any signalling. You can even connect an external audio source like a CD player and "broadcast" your own content. And while it is in this mode, the HP8922 can also receive speech traffic and you can hear it on its built-in loudspeaker.
The benefit of this for getting the Layer-1 code on the phone right is that you can concentrate on TCH receiving and transmitting without having to care about signalling. You just "tune" to the right ARFCN and timeslot (I don't use hopping during testing) and see that you get your code running.
I guess that having this special mode (setting an ARFCN and timeslot and "listen" to the TCH) in the phone can be quite useful for debugging non-hopping, non-encrypted, single ARFCN cells like OpenBSC and OpenBTS.