I went from an HTC HD2 to an iPhone 4 and I never regretted it. WinMO 6.5 is so laggy so I installed Android 2.2 on it and it was 100x better. I now bought an iPhone 4 unlocked it and using the same sim that was from the HD2 and works fine. Highly recommend the iPhone 4 but be on the lookout this might be the last model you can get on T-Mobile since it's most likely the last one to use sim cards. Rumors are floating since the new Verizon iPhone has the Qualcomm CDMA/GSM antenna it can run both Verizon's and AT&T's network without the use of sim cards. Thus making the iPhone IMPOSSIBLE running on T-Mobile