PSP VITA (NGP) game type?

i have looked around and have not seen any news on what type the games will be. are they UMD's, download only, game cartridges like the ds? i am wondering because it might be the deciding factor on whether or not i get one. and also, it the 3G version going to be at&t ONLY or could i get it switched to verison? im getting a new phone soon and it is going to be with verison and i would get a 3g version if i can link it to my plan but if not them im just getting a wifi version. and i probably will not get one at all if it is download only beuause i dont want a bunch of games taking up space on my memory card. and also... what is the capacity of it? the GO had 16 GB. does the VITA have any internal memory at all? if anyone has seen something about any of these topics, please let me know or send me a link to the info. i might have missed it