What features do not work on an I-phone flashed to be used on the MetroPCS network?

I have heard that certain features will not work such as Visual Voicemail and certain internet based applications. Is this true? What do i need to do if I have an unlocked Iphone and I want to use it on the MetroPCS network?

Which iPhone? The latest models ( from the 5s at least) will work on any network without issue. If you have an older model, then MetroPCS is probably not an option any more. MetroPCS used to be a CDMA network running on top of Sprint. That changed several years ago, and they now run under T-Mobile's GSM network. So if you have an iPhone 4 for a CDMA carrier like Sprint or Verizon, it just flat will not work on MetroPCS.