Carphone Warehouse is launching its "iD" mobile network tomorrow, and in preparation it's revealed new details about its contracts and how they differ from the competition. For starters, they'll be separated into four tiers: Shockproof, TakeAway, Go To and SIM Only. The Shockproof tier starts from £7.50 per month and is designed to help you avoid expensive bills. To do this, iD will cap your usage automatically, while offering a customisable "buffer" just in case you find yourself craving a few extra GB. TakeAway, meanwhile, will offer plans from £25.50 per month with free roaming in 22 countries -- that's more than Three's "Feel at Home" initiative, if you're keeping score.