One day there were some fairly intelligent guys sitting around a table, trying hard to think of a company name, and the best they could come up with was ‘giffgaff’. True story. Rubbish name aside, giffgaff has a fairly sweet goodybag containing 250 monthly minutes, unlimited texts and proper unlimited data, all for £10 per month.
giffgaff is an exclusively PAYG network. No contracts.
If you use up your 250-minute allowance, calls are 8p per minute to mobiles and landlines. giffgaff to giffgaff calls are free (now there's a sentence we never thought we'd write).
(Thanks to SamuraisShadow on HUKD)