novice at upgrading/renewing contract

medindexer

I have a mobile for my son and am nearing the end of the year for his e2save cahsback contract (a free Samsung D900 with 250 calls + 100 text per month with 02). All went well with cashback and it cost in the end £120 for the year. I'm a good negotiator but I'm confused at the options.

Presumably I could just end the contract (and buy a new phone with a similar sort of deal from e2save who I must say I've been happy with). I gather he gets to keep the old phone (am I right)?

However, what if I enter the negotiating-over-the-phone route to get a new contract? Is the negotiating done with e2save or with O2 (or is there a choice even). I've seen the advice about how to negotiate. Is it best to ask for an upgrade phone? Does he get to keep the old phone or do they ask to send that back? Should I aim to obtain at least as good a contract as the one before and do they offer cashback contracts when upgrading. There's a lot I'm unclear about. I'm sure other have asked these questions before, but some fresh clear advice would be appreciated. Thanks