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.
So, if you are working with a real estate agent, talk to them about whether using a letter of intent would be better with the offers you are making or if they want to continue to write up full contracts for each offer.