My current plan:
AT&T Family Share 700
$60.00 base plan
$30.00 unlimited texting plan
$29.97 additional line fees ($9.99 per line x 3)
$120.00 data ($30.00 per line x 4)
= $239.97 TOTAL
That is, if I've done all that math properly. AT&T has so many programs going (Mobile Share, Next, keeping 2-year contracts on the table, etc.) that I'm always afraid I've overlooked something that's going to bite me in the end.
You need to factor in the price of the phones into your current plan so add whatever the subsidized price of the phones x 4.