A LOI is typically used as a "starting place" for negotiations on a property. Generally a LOI will be followed up by a formal Purchase Agreement after the terms are settled on. This may or may not be the case in your area, but is a good use of the two documents.
If you are a landlord or a property owner and have been approached by a cellular carrier or cell tower developer about putting a cell site on your property, here is the rule for dealing with tower companies or carriers who try and get you to sign a "Letter of Intent"....... DON'T SIGN ANYTHING!!!!!!! Call your counsel or better yet call a qualified wireless consultant that can guide you and fight for your rights and needs. The carriers have experts...why shouldn't you?