I just read somewhere that someone took in a coupon accidentally from another store to Jamba Juice and they accepted it. So i just called 3 of my Jamba Juice's and was told by all 3 locations that yes, they would accept a competitor's coupon such as Juice it Up, McDonalds, etc as long as they have a way to input the discount on their register.
It is not store policy to do this but rather a courtesy.
So don't disregard other coupons thinking you can't use them cause Jamba Juice is there to save the day.
Juice It up has a coupon right now for a BOGO smoothie. You can either redeem it at Juice It up or try to redeem it at Jamba Juice - whichever is local to you or more convenient.