Yes. Its pretty easy and has been asked before. If you both are ATT, they will merge them and one just picks who takes the main plan and financial responsibility.
Most of the phones I looked at when I was switching around that had Qwerty keyboards had Windows Mobile and were smart phones but it might be worth looking at www.att.com for some online deals.
The SIM card is cool. You can save your contacts to it so which is kind of limited. Just Name, Number, and Type of number but you can put it into any ATT phone or unlocked GSM phone.