Question about MagicJack phone line?

My 95 yr old mom just moved into assisted living and we got her a new phone and phone number because its out of the area and we can't transfer her existing phone. But we want to keep her old phone number that she has had for almost 70 yrs. Can we install that thing called a "Magic Jack" so we can eliminate her monthly phone bill for a phone that will no longer be used? But if and when she comes home we sure want to have that same number. Thank you.