Best Buy will do it, but they charge $30 for the kit and then $13 for the install. The total price is pretty steep. If you check the Zagg website for locations, you might be lucky enough to have a Zagg Mall Cart close to your location. That is the best option since they stand by their work, and you can visit that cart if you need a replacement. Alsl, the kits sold at Best Buy cover the front and the back of the phone only. The ones sold at Zagg stands cover the sides, bottom, top, front and back.
I've used the Invisishield on my iPhone, iPhone 3G, iPhone 3GS, iPhone 4, iPad, iPod touch, iPod nano, iPod classic, and other gadgets. I love the product and recommend it to anyone. Best warranty, high quality, no gunky residue on the phone, and Zagg will stand by the product. Adds nice grip to the phone, and allows NO scratches or dings. Worth every penny.
Sorry for the long post!