Rumour has it that GSM will use Boeing 737-700's, probably wingletted ones. They don't actually have this type in their fleet at the moment but have two on order, one to be delivered in February 2007, the other in Spring 2007. It is currently unclear whether these are brand new or second hand, if second hand, they will most likely come from easyJet who are to begin getting rid of theirs soon.
Regards,