Crown Castle, a company that recently purchased over 6000 leases from T-Mobile, is now sending out letters to their lessees introducing themselves. They are asking lease-holders to sign and return those letters. If you or your clients have a cell tower lease with T-Mobile, consult with an attorney before signing.
In short, the letter is asking that you waive or confirm that there are no defaults or other problems with your lease.
The letter may look innocuous, but be cautious. Check with your attorney first.