I have 2 LTE phones, one on ATT and one on VZW...both get great reception (full bars) at ATL airport....neither gets great data speeds (to the point that it's a huge drain on the batteries and impossible to do anything involving data)......I've always assumed both ATT & VZW circuits from the towers are maxed but who knows I guess (I'm sure if I asked a front line associate in the airport someone would tell me they want me to use the airports wifi service too)

Personally I highly doubt Marriott would be blocking anything after losing the case with the FCC