I just got one of these from Best Buy about a gift card. celloptout.com might be a scam, as https://www.donotcall.gov/ already lets you opt out of telemarketing calls.
I looked up the domain name info and found that celloptout.com is hosted at "bahamamoney.com" so that sounds pretty fishy.
Had TWO text messages today, one at 1:52 AM and the other at 5:32 AM. JUst got a new mobile number last week and Ive been bombarded with this crap since day one! Message reads " Test and Keep and iPhone 5! The first 1000 users that go to http://cell-rewards.com and enter code: xxxx will qualify. Optout at celloptout.com." This was sent via two different numbers, one was 520-366-4282 and the other was 406-208-4607. Have filed a fcc complaint and next will be demanding cell provider provide blocking software for this ridiculousness!
I got the same message about an iPhone, at 5:00 am. I texted "stop" back. Later in the day I received the same message from 406-208-4607. Both texts were just like what everyone described above, instructing me to opt out at celloptout.com. Their site looks phishy.