1 - Look at the N900. Is it an N900? Congratulations - it's unlocked!

2 - Texts are always the same on all plans. Cross-network calls are generally more expensive than same-network calls when you're on pay as you go. Unless you have a free calls allowance, of course. Check the terms.

3 - Ebaying pay-as-you-go SIM cards is expensive and dodgy. Get free ones direct from the network:
O2 http://freesim.o2.co.uk/
Vodafone https://www.v-store.co.uk/index.cfm?...ckout.freesims
3 http://www.three.co.uk/Pay_As_You_Go/SIM_Only
Orange http://freesim.orange.co.uk/
TMobile http://www.t-mobile.co.uk/shop/free-...-go-sim-cards/