...

But I guess you can use two MSs, one for transmit and one for receive to overcome this limitation. Is there any problems with this approach other then good clock synchronization?

You need a very good clock sync :) But that's something that could be tried I guess.

maybe.. you could sync the "receiver phone" to the "transmitter phone" by using one timeslot. (TS7) or you could sync the receiver phone to a nearby bts and use a control line on the serial link to sync the transmitter phone to the receiver phone. (you need to cross-connect the serial ports on the phones for signalling anyway.) andreas