Found this offer attached to the credit card terminal at my local Staples yesterday. Text "JOIN" to 555-444 and you will receive a $5 off $25 coupon. It actually sends you a link that you use to sign up for their mobile offers list. The coupon arrived 24 hours later. There was an earlier thread for a $10 off $30 coupon. I did that one, and also was able to do this one.
The coupon is valid in-store only and claims to expire on 3/7/14 (I guess we'll know the real date when someone uses one and looks at the receipt).