So the answer to the original post was yes here for an amplified one:
Amplified Mobile (Cell) Phone Adaptor - Adaptors - Pilot Warehouse'ASCO
or here for non amplified:
GSM Cell Phone Adapter @ Flightstore Pilot Supplies
Though it comes with a note: "We do not promote or advise the use of this equipment during flight."
I wonder how many of the posters above have used a mobile phone at some point while driving where I'm sure you will agree, the consequences can be just as bad and maybe even more likely! (Not condoning use of mobiles in flight before you go off on one!)