Quite possibly the best way to sum up what Apple have been up to.It was always going to go this way. Just as it was with the iPod.
Phase 1) Offer exclusive product that everyone wants for a huge amount of money. Only early adopters will buy it and those with enough cash to flash but it will seal the product's exclusive fate as must-have item. This is exactly what they did with the first iPhone.
Phase 2) When mass-market appeal is needed to fuel growth - and when competitors are starting to produce copycats at much reduced prices - it's time to lower the price and open up to the mass market. Here you can expand the number of territories available too (and in the case of the iPod, allow Windows users in too). This is the iPhone 3G.
Phase 3) Accelerate growth by offering it in as many places as possible and further refining the price model, add new versions. This is where Tesco comes in. They now need visibility for all those people who say that phones are just for 'calls and texts' - the kind who swore in 2003 that they never needed a mobile phone - and who are unlikely to walk into an O2 or Orange shop. This is now about keeping up momentum, including branching out to other networks.
The iPhone's exclusivity is wearing off now - every Tom, Dick and Harry has one - so don't limit its growth by only offering down a select few distribution channels.
I just hope Apple bring phase 3 to our American cousins so they have more choice!