ok, it looks like we have some confusion between terms here. AT&T data plans have a few differences and they also have a few product lines.
AT&T Hotspot / AT&T WiFi - This is AT&T's Wifi network. iPhone users can get on for free, and any wireless data plan over $30, and any U-verse customers have free access to AT&T Hotspot / AT&T WiFi. This is a WiFi only network. There are also subscription services which are $19.99 per month for this service.
AT&T Wireless Mobile Broadband - This is AT&T's LTE/4G/3G/EDGE network. This is what you normally get on your smartphone or tablet device. There are multiple sub-plans depending on what you need.
AT&T Data Connect Tablet 2 year contract - This is a contract tablet rate. 3GB is $35 and 5GB is $50 per month. Overage is $10/GB.
AT&T Data Connect Tablet No Commitment - This is a non-contract tablet rate. 250MB for $14.99 with $14.99/250MB overage, 3GB for $30, and 5GB for $50 with $10/GB overages.
AT&T Smartphone Data Plan 5GB - This is the only tethering data plan that AT&T has. It costs $50/month and overages are $10/GB.
Hotspot != Tethering