I regularly use 3UK (Hutchison)'s data service. £10 gets you 15GB of xfer a
month, but you need to either sign a contract or else pay £50 for the
hardware, which as with most UMTS operators is a Huawei E220 USB dongle.
That particular device currently supports radio air interfaces from GSM up to
HSPA 7.2Mbit/s. There is support for the E220 in current Linux kernels.
However, 3UK (and most of the other operators) ship it with a Windows client
program installed on the USB device that autoruns when you connect it to a
computer. This provides a "pretty" interface to it. Unfortunately, it also
means that unless you activate the device at once, under Linux it gets
detected as a USB mass storage device not a tty. You can get around this if
you connect it before booting; I think there is a modprobe or similar
operation that has to happen, so there is almost certainly a command-line
workaround.
If it is working correctly you should be able to see three new ttys in
/dev/USB. You can then use whatever program you like to dial up, or just run
wvdial. In my experience 3UK works reasonably well; they advertise maximum
speeds of 3.6Mbit/s downlink, but I've seen higher in practice. The uplink
seems to max out at 600-700Kbit/s, which is considerably better than my DSL
line. IPs are dynamic, and things like Skype pass through without trouble. I
have successfully SSHd into a linux box both from a PC over the modem and
using PuTTY from a Nokia E71.
Warnings: 3UK's DNS could be better, when I am using their service from a PC I
usually set up OpenDNS. On the move, you may encounter problems with the step-
down between UMTS and GPRS; 3 gets its backup GPRS national roaming from
Orange and you can easily lose a connection between the two.
T-Mobile UK was the first UK operator to provide open slather Internet service;
they offer a higher level of "unlimited" for a price, which includes not
blocking VoIP and a static IP. Otherwise expect similar to 3, as they are
beginning to share their radio access networks.
Vodafone probably has more coverage than anyone else, but their Internet
service may not be to your taste. When they started doing pure 'net, they had
a restriction on Web pages over 200KB and pushed everything else through a
Novarra box to compress it, which broke a lot of things; I once got a header
in my blog server logs that mentioned an XMS, a Novarra, a squid proxy and
something from 724 Networks.