Doc Holliday said:
It's also not wise to use the hotel's phone system when a particular hotel is possibly under police surveillance. Quite often the lines of communication in a particular area under surveillance are being "monitored". But heck, even cellphone conversations are easily monitored by using a good audio scanning system.
Phones can't be monitored at random, a name and a precise address must be on the warrant. LE can't listen to all phones in hotel just in case they catch somebody. For an incall, this could be different if they always get the same room and spend hours there. Within the time you spend with an outcall escort, they have no way or time to get all required stuff set-up from both the legal side and the technial side. Remember also, there's no problems with the law to have an escort visit you in your hotel room so, why would they monitor you to start with?
For cell phones, unless I'm mistaken (possible but unlikely), I suggest brushing your telecom skills.
New phones use digital signals, data encoding and frequency multiplexing, making run-of-the-mill scanners useless. With older phones, a conversation would possibly hop from channels to channels while you were talking but, it was a plain analog transmission so, it was possible to follow with a good scanner and a bit of work. Now, what's sent is a digital signal, with no analog component beside the radio wave itself. Before listening to it, it must be decoded. On top, while the frequency hopping is still there, the multiplexing allow multiple peoples on the same channel at the same time. In order to listen to a conversation now, you have to decode the digital signal from the air, know what's the electronic ID of the phone used by your target, separate this ID from the data string who includes everybody else plus system signals and then, recombine it with the proper timing, ensuring your decoder can follow all frequency hops.
It's not impossible to listen to a new digital phone but, it's very complicated so, whoever was having fun with a scanner likely won't make the steps required to listen to a digital phone. Must be expensive but of course, cops can do it: we're the ones paying the toys for them!