UK data tariffs (as of January 2008)

All of the main operators offer data packages: T-Mobile, Vodafone, Orange, O2 and Three (3, owned by Hutchison-Wampoa).

I'm on T-Mobile with their Web 'n Walk data package along with my Flext call package, and I've got to say (aside from them blocking port 21 late last year, which is avoidable if you just SSH into a server then tunnel through it) that it's pretty much flawless. Although they say otherwise, nothing else is barred - with my HTC Hermes (Vario 2) I can use it as a modem for my laptop (tethering), I can stream video and audio, I can use IRC, I can even use Skype (when I do use Skype Mobile, about once a year!). If I was planning on using these services more, I'd move to one of the higher tiers, but I'm happy where I am right now. I managed to get HSDPA provisioned on my account too, and I get blazingly-fast speeds in and around Birmingham (UK, where I live).

The allowance on the base WnW package is 1Gb a month for £7.50, but the nice thing is that if you go over your allowance for several months running, you may get a note via email or a call saying "please don't do it again" (or you may not), but they aren't religiously strict about overages.

From what I've heard, O2 (with their 1Gb package) and I've heard various things about Orange's "Unlimited" package (for £8 per month) including mentions of caps ranging from just 30Mb per month to 4Gb per month fair usage. I've never been an Orange customer though, so take that at face value. Orange have historicallly been very expensive though. VoIP, streaming services, instant messaging, and modem access from your laptop (aka 'tethering' is also apparently barred, which is a big pain in the arse for casual users like myself, that's why I like Web 'n Walk so much.)

Vodafone's £7.50 a month data plan gives you 350Mb fair usage per month - just over a third of what you get on T-Mobile. Similarly, O2's "Web bolt on" is £7.50 a month for 300Mb. Not a lot, really.

3 offer the most flexible set of data plans - their base package is just £5 a month for 1Gb, and their data cards and 3g modem packages (exclusively for PCs) are the cheapest - my mate has a USB 3G modem just for his laptop, which doesn't cost a lot at all. If you have a phone package with them, the addon for 1Gb of data is £5 a month (though I suspect they block VoIP as they promote their own Skype deal as part of their X-Series tariffs, which in fact works in an identical manner to EQO's own service - dialing a Skype access number to actually place the calls, thereby falling back to the 2G network. Three also charge for overages (but not as much as other networks!)

So, in summary, from personal experience I'd have to say that T-Mobile's offerings are the best - they don't have any overage charges and their allowances are quite generous for the price. I'm happy to stick with them for another 12 or 18 months after February (when my current contract ends).