can I call the USA from Rome, Italy on Verizon iphone 4

you can call anywhere you want, but be sure to check the cost.

No. Italy uses a mobile technology called GSM, with is the standard throughout most of the world. This is the technology used by AT&T. Verizon uses an alternative technology called CDMA that is incompatible with GSM and non-existant in Europe.

The Verizon iPhone 4 will operate in most of the USA and Canada, many parts of South America, Asia, and much of Africa. Conversely GSM won't operate in about 1/2 of Africa and Greenland.