iphone 4 on tesco

[Big G]

Tesco seem to have some really nice deals on the iphone 4 at the moment. Much be appealing than orange who I'm with now...

£20/month
12 month contract
250 mins
unlimited texts
1gb data
phone cost is £349 / £429 respectively.

I would prefer to stay with orange as I've been with them for 12 years now and I think I get a 20% discount on my line rental for my loyalty, but the cheapest they offer is £30/month on a 24 month contract and only give you 150mins/250texts. Phone costs are cheaper, but that's outweighed by the long contract and being locked into paying £720 over the 24 months

Is anyone else with Tesco and can give their opinions on it? I understand they share the O2 network so coverage shouldn't be an issue.