Straight Talk, Bring your own Phone SIM Card - $15
$45 monthly for unlimited (Soft cap 2G) 3G; Talk, Text (Yes Text, unlimited too)
All using ATT's post-paid network antennas.
Oh, and if you JB and install Tetherme, you can use Native Hotspot Feature for free, and provide wifi to other devices.
ST Sim: $15
ST monthly: $45 (x 2 years) = $1080
TetherMe - $10 one time
iPhone 4S = $649.
Total 2yr Package w/ hotspot= $1754
ATT Total 2 yr package with hotspot: $1,000,000,000.
With a family plan AT&T can be similar price. I am not going to compare your tethering because you are probably violating your terms of service, whether StraightTalk is checking or not.
Family plan 2000 voice minutes with rollover: $99
4 extra lines at $10 each: $40
Unlimited text (also gets us unlimited voice minutes to ANY mobile): $30
3GB data plan at $30 each: $150
Monthly cost: $320
2 years service: $7,680
iPhone 4s: $199 * 5 = $955
Total for 5 phones: $8,675
2 year price per line: $1,735
This is pretty much what my actual family plan looks like except our data plans are 2 GB, 2 GB, 300 MB, Unlimited, and 4 GB w/ tethering for a total of $145 monthly for our data plans. With unlimited mobile to mobile we never use many of our minutes, we currently have 11,000+ rollover minutes, so that is practically unlimited voice.
Not everyone can get the ideal 5 people on one plan, but the per line cost is pretty much the same as your StraightTalk example.