My friend bought T-Mobile G1 Android mobile phone from T-Mobile Czech Republic (i.e. standard, non-rooted, white version).
My friend had problems with the phone. It locked up without reason, repeatedly. He went back to T-Mobile and the phone (still under warranty) was sent to the repair shop.
After one day in the repair shop, it was back, supposedly "repaired", with the following priceless explanation from the repair technician:
"Malfunction acknowledged. The phone uses highly unstable Android system. Repaired by completely re-installing Windows Mobile. Restored factory settings and tested in GSM network."
Note that this was done by official T-Mobile repair service! Below is the scan of the actual service report (click for large):
However, it seems the service technician overestimated his haxx0r sk1llz. When my friend tried to turn the phone on, it just cycled between "T-Mobile" and "Android" logos ad infinitum, without booting. So they took the phone back again, noting that it was probably "not fixed".
Maybe they will now give him a new G1 phone but personally, I'd wait first, to see if they will be able to install iPhone OS on it...