Is MetroPCS "flashed" iPHONE going to be different than the regular iPhone features/apps?

[Elyza]

I used to have AT&T service on my iphone and now I am wanting to switch my service to MetroPCS. I was told by a MetroPCS agent that they can unlock and "flash" my iPhone by putting in a new Sim card to make it work with Metro pcs service. (I hope this method is not the same as what people call "jail hacking" because I heard jail hacking is bad and can make phones vulnerable to Malware, mess up the battery, etc).

Q) I just want to know, if I do that, will there be any difference in the Apps which I can download on the phone (can I still use apps like Instagram, twitter, Tumblr, skype, facebook, and games, etc) ?
..... and will I be able to download more app's from apple store just as I would if i had my AT&T service.. OR will the app's on Metropcs be restricted and I would have to use an alternate Metro app store to get those apps ( in which case, would they even be available)?


* If anyone has flashed their iphone from ATT to Metropcs, can you please advise any differences there may be, any Cons associated with this change? *

The last thing I'd want is to risk damaging my iphone by making it susceptible to any malware and such.