[obsessive1]

One of the problems in the UK is that it's hard to find an unlimited internet plan. Nearly all the networks place a 500MB limit, which is very easy to go over if you use tethering apps. It can end up costing an absolute fortune.

[semanticist]

While there's no truly 'unlimited' packages, my standard data with T-Mobile is 1GB, and you can usually find packages for more if you need it.

If you're using your phone's internet a lot, it's probably better value to get a USB dongle or mifi device. You can get a 3GB/month contract from Three for £10 or £15.

[shrikant]

I'm visiting the UK from India, and I can confirm that it is not just hard - it is impossible to get an unlimited data plan. Among all the service providers, there are only two that even advertise one, and even that says "3 GB fair usage per month" (wtf?!) in the fine print.