O2 Refresh

[TechnoJohnUK]

OK, so I'm reasonably set on a Nexus 5, on O2 (who I'm with at the mo). The question is, who do I get it from? Someone in an O2 shop told me about "Refresh" which seems interesting - a certain amount of your monthly bill goes towards paying for the phone, and some to the line rental etc. Once you have paid off the phone part (You can pay extra amounts whenever you want), you can change your phone, and if you want to go to a different carrier, they waive the rest of your airtime bills.
One thing is, O2 want

 

[Rukbat]

That's how it works with all carriers in the US now. (It used to be just a subsidized price up front - which, for a simple feature phone or the lowest level androids, would be free. Now you can do the monthly payment toward the phone price (which usually ends up being a bit more total than the outright buy price of the phone).

As for unlocking, we have 2 main GSM carriers in the country - one will unlock after 30 days, whether the phone is paid off or not. The other MAY unlock if you're traveling outside the country, but people have had problems with them. If they promise to unlock under certain conditions, I'd ask for it in writing, until the plan's been around long enough to know how good they are with unlocking.

Or, if you can afford it, buy the phone outright, unlcked.