From what I understand you want to transmit on the GSM frequency and place noise on it!!! This is illegal and really out of the scope of a hobbyist! It would require some very sophisticated digital technology!
Maybe I have missed the point, but why do you want to add noise to it anyway?!
1. bend over
2. insert into rectal cavity.
3. look stunned
But seriously, I don't think its possible without lots of sophisticated equipment... maybe you could make a high voltage discharge device -- that seems to **** up mobiles a bit.
There is already a device used ( mostly in the Mosque & church ) that blocked GSM signals but these are used with a permission from the authority not just by anyone .