AT&T's current Mobile Share plans can be quite expensive for families and small offices that don't want to be tied to a contract. However, service is potentially more affordable through a new plan launching Sunday. The tier starts at $130 per month with two off-contract lines for new customers (existing contract customers can also sign up) and 10GB of shared data, but it costs a more modest $15 per extra line instead of the regular $25; the carrier reckons that a family of four could save anywhere from $40 to $100 per month over the regular rates. You can go for more than 10GB of data if your clan craves extra bandwidth, too. It's not clear if AT&T's deal will be enough to lure families away from low-cost carriers like T-Mobile, but it's certainly a better offer than before.