AT&T just announced an upcoming Mobile Hotspot app which will allow a compatible device to share its data connection with up to 5 devices via Wi-Fi.  At the same time, changes to the company’s current tethering plan will also go into effect.

Currently, smartphone users who pay an additional $20 per month are allowed data to use with secondary devices (like laptops) via their tethered smartphone, but that data is deducted from smartphone’s own data allowance.  After the change goes into effect, customers will still pay $20 for tethering, but an additional 2GB will be added to the 2GB of data provided with the Data Pro smartphone data plan, for a total of 4GB of data across all devices for $45/month. Tethering is and will continue to be limited to those on the Data Pro plan ($25/month), and will not be available with Data Plus ($15/month) or the grandfathered unlimited data plan ($30/month).

All of this goes into effect on February 13, alongside the release of the HTC Inspire 4G Android phone.  Since the Mobile Hotspot app will likely be Android-only based on the wording of the press release, it’s unclear how this app differs from the built-in hotspot capability already included in Android OS 2.2 and 2.3.

Users already paying for tethering from AT&T will receive a text message when the plan changes to into effect.

You can read the full press release here.