It’s official: AT&T is FINALLY launching iPhone data tethering in the United States this summer, with the launch of iPhone OS 4. The iPhone is getting a new data plan that offers tethering as a $20 per month add-on.

Existing iPhone customers will have to drop their $30/month unlimited data plan for a new $25/month 2GB plan — plus cough up an additional $20 per month for tethering. That’s in-line with what the other cell carriers charge for tethering, but having to change plans is annoying.

From AT&T’s press release:

Smartphone customers

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