A “MMS transfer” is using several timeslots on one TRX (in UL or in DL, depending if the MS is sending or receiving).
Those timeslots are not specific to GPRS, they are either used as TCH (logical channel to carry voice) or PDCH (logical channel to carry data). It all depends on the demand. So OK, the name of the logical channel is different, but the physical channel is the same : 1 radio timeslot.
One radio TS can carry different type of logical channels, for instance TCH or PDCH. However, but don’t take it as a rule, it can happen that one operator defines 1 or 2 TS as pure PDCH, statically.
MMS is transparent for the radio part : it is seen as “GPRS traffic”.
I hope it answers your question…