Here is another question for you. Why would anyone try and get you to sign anything unless it is binding and could be used against you in a court of law? There is no other reason.... this is the reason they try and get you to sign this. The only person that is being locked into anything is you and usually in a way that is very one sided and only benefits the carriers and the tower companies.
For example, I usually buy houses directly from sellers, but last week I started to make some creative owner financing offers for some houses through real estate agents. Once I was able to talk to the agents representing me, they immediately saw the benefits of my offer to some sellers. Unfortunately, the agents I talked to would be presenting my offer to another agent that represented the seller.