AT&T just announced a partnership with Apisphere to sell a dog collar with a SIM card inside so you can wirelessly track your pooch.
The collar works by you setting up a "geo-fence" around your home where you want your dog to stay. If it leaves that area, you'll be notified. It uses GPS and cell service so you'll be able to pinpoint just where Fido has wandered off to. It's cheaper than installing an invisible fence, I suppose. [AT&T]