I have an LG P505R. It was locked to Rogers. I purchased a set of unlock codes, and entered the appropriate one - it says the phone is unlocked.
All is well when I use a Rogers SIM. However, when I install a T-Mobile SIM, I get the error: "The process com.android.phone has stopped unexpectedly. Please try again. Force close." every two seconds or so. Practically makes the phone unusable!
I would have said it was the SIM chip - except that this SIM chip works in a V3, and V3i, and a Samsung Galaxy SGH-i896 with no issues!