first make sure that phone is GSM quadband, and works in 800-900.... I don't think verizon phone works in nepal. but make sure first.
you need to unlock that phone, if it uses SIM card, eg TMOBILE then call their customer service and tell them you need to unlock the phone since you are going to use that phone in other country with different service providers. i did that once, they send me unlock code and did it rightaway. that is the easiest way, spending without a penny.
other way is, take your cell phone to any dhoti ko cell phone pasal and tell them to unlock it. they might keep your cell phone for 1 day or in the same day but they will charge you price ranging from $ 10 to 25.
One more way, I heard but not sure. you can get ur phone unlocked even in nepal these days.
other way, you can search for the internet sites which charge like 10 dollar to unlock the phone. it may or may not worked.
maybe this will help you,