I am trying to use my O2 PAYG 2G SIMcard in this phone until I get my hands on a 3 SIM, but when I switch the device on it just says 'Invalid Card'. How can I get this to work with my O2 SIM?
You cant unless you pay someone to unlock it. This and all 3 phones are SIM locked to thier network as are most other handsets supplied these days.
3Pay USIM's are available on E-Bay for about £12-15 and will solve your problem if you can get a useable service from 3 in your area as the e606 is not very good on their network.