These excellent little portable WiFi Mobile data devices seem to be available again from Tesco Direct.
These come with a Vodafone data SIM providing 4 Gigabytes of data which lasts 30 days after activation. (Update.. according to allan1954, the SIM only comes with 2Gigabytes of data and not 4 as stated by Tesco. I cannot confirm one way or the other regarding this).
These are 3G (or slower) only. Not 4G enabled, however at this price you can't go wrong with up to 21mbps download speeds.
They are Vodafone branded (not my favourite company at the moment), and come locked to the Vodafone network.
However for 99p they can be unlocked with a code from ebay. (Just search for R207 Vodafone unlock code).
Also, after unlocking, remember to go into the advanced menu and setup the APN for whichever network you are intending to use as the default APN is set to Vodafone.
eg. Using EE data SIM: Set (in Mobile Broadband - Connection menu)
ACCOUNT TYPE to Custom
IP Type to IPv4 + IPv6
IPv4/IPv6 APN to everywhere
IPv4/IPv6 Number to *99#
Security to CHAP
Complete UK APN list here ..... http://www.mobilez.org/support/apns/uk/
For the three network... It is the same as the APN setting for EE, except put " three.co.uk " instead of " everywhere " all other settings are the same. (thanks to Inactive for that info)
info supplied by wildecat follows...
O2's APN is usually either:
mobile.o2.co.uk with a username of mobileweb and a password of password
m-bb.o2.co.uk with web as both the username and password
The correct APN for 3 is 3internet not three.co.uk as this is for mobile handsets