Hi
Jamming of mobile phones is easy enough (if you dont want to cover large areas) but it is illegal in the UK, even though the equipment is avaliable on the internet.
A mobile phone jammer will cost you anything from £100 upwards and it will also knock out the GPRS/Data side as well.
Here is a link to a story about a hotel in Scotland jamming mobile phones to force folk to use the hotel phones.
http://makeashorterlink.com/?H2BF1271D
Very interesting reading
regards