I got my current phone from buymobilephones.net with a free iPad - the service is brilliant and I would highly recommend them. I'm going to upgrade through them when my contract is up in February x
I would be very careful when upgrading through them. I work for a phone network and nearly all people who take contracts from lesser known companies that are upgraded are given a knew contract and don't know they are paying for two for months.
If upgrade through them, confirm everything they say to you and ensure you read the paperwork/emails within your return time just there is something wrong.