AT&T's site was so screwed up that I ended up going into a store to get it done. The web site insisted that I needed to get a new data plan in order to get a Series 3. The store didn't know what that was about, and they had no problem selling me an S3 under my current plan. They also explained (as others here have) that the watch is assigned it's own number, but once you get it, you can link it to your phone's number.