Basic car phone questions

[Scott 20191668 Bermes <scottb2460@earthlink.net>]

The 92 100CS I recently purchased came with a Bell South Mobility car
phone.   I turned it on, dialed *611 and got the cell phone company
Alltell.  Dialed my mothers number then got a recording asking if I
wanted to pay by credit card, calling card or who my cell phone carrier
is.  

Is it safe to assume I could put this phone system in my wifes car
(deinstall in mine, reinstall in hers) get a phone debit card and let
her use it for emergencies?  I don't want to get involved with another
monthly payment for a cell phone carrier.  Appreciate any info.

Scott