I’ve been in Canada since October, and have an LG Optimus One on Koodo. However, i’m back in the UK next week. Can I bring this phone with me, and pop an O2 sim in or is it incompatable?

It has a an option for “preffered network mode”- currently set to GSM/WCDMA auto.

Any ideas or do I need more info?

If buying here I think you need a quad band phone to work over there.

No idea how it works the other way, I’d ask over there.

It’ll depend on your CA network; some of them (incl Wind) operate on really weird frequencies that are used nowhere else except the US. Calls and the like will be fine, but data can be an issue – because they’ll often work with up to 4 GSM bands, but only 1 3G band.