I have a similar question. I'm flying to the Netherlands for a week. I do have a T-Mobile SIM for the Netherlands, as I lived there for a year, and still have a plan there (just call time). Wondering if it is worth unlocking my phone for this and then relock it when I return. I'm running 1.1.4. How would I go about unlocking it? Or would it be better to just use my old unlocked RAZR and use the iPhone as an iPod? Thanks for your help.
For you, I would recommend unlocking. The OP looked like they did not need/want phone service while there, so unlocking did not seem like a good proposition for him. For you, though, you seem to need ot want phone service- the only way is to unlock. Then you should be just fine.
Unlocks have come a long way-you CAN reverse them if you want "no trace" left". I would recommend the iPlus unlock for you, they d/g the BL to 3.9, but with a special hack so you can upgrade it back to 4.6 when you are done. (I am not sure HOW to upgrade it back- that is a GOOD question!)
For me, since I am T-Mo in the US, I am just get a local pre-paid when I am over in Europe. Seemless.