In the UK there are 4 big providers, TMobile, O2, Orange and Vodafone. To be honest they are all pretty close from a tariff perspective. Some had a few minutes more and few SMS less or vice versa. TMobile had a unique service whereby you had a credit "bucket" and your minutes, SMS and MMS all came out of the same bucket meaning one month you could have 499 minutes and 1 SMS and the next month 499 SMS and 1 minute etc. I doubt they'd have to change much to enforce this price promise as the plan itself is so flexible. All they'd need to do is increase the "bucket" size.