Adding Cingular family plan

[MrsC]

Hi everyone,
I have the Cingular Nation 350/3500 plan from a couple of years ago which I would like to stay with if possible. I'm using a Nokia 6340i GAIT phone. I would like to add another phone line to my account, but I would like to keep my plan because it has all the minutes I need and costs $39.99 a month and is nationwide. The new Nation GSM 450 Family Talk w/rollover comes closest to my current plan, but the GSM coverage is not anywhere near as good as the GAIT plan. The GAIT plans currently offered would cost another $15 a month for comparable minutes. I travel from Missouri to SW Arizona on a regular basis and can currently use my phone in most areas I go to. The GSM map looks pretty spotty in comparison. My question is this: Can I add another phone line for $19.99 and share the minutes of my current plan, or will I have to change plans? Also, I have another 6340i without a SIM card, so if it's possible to add another line, all I would need to do is get another SIM card and have the phone activated, right?

Thanks to all who respond.
MrsC