Can an At&T Motorazr be used on an Alltel Account?

My friend uses Alltel as her wireless provider. She had a Motorazr but dropped and broke it and she doesn't like the replacement phone they gave her thru her insurance (not another Motorazr). I have an AT&T Motorazr just like her old one that I no longer use and would like to give it to her. She is afraid she won't be able to use it with her Alltel account. Can she use it? If so, is there something special she has to do first like unlock it? She said she tried several years ago to use a phone from one carrier with a different carrier and they refused. Have things changed any over the years in this regard? Thanks for any help or info!