A nice little thing to have added would be static proggy-like payphones. Give each one a number that can be got by looking at it, probably written on the box somewhere. Cool for when you wanna do dead drops with a client, or organize shady biz, but don't wanna call someone directly and risk giving away your digits.
On the flip, you can also use them to anonymously call folks, but they charge a bomb to use, like 100c a minute or whatever. Useful for when you're without a phone, or when you're wanting to harass that corpie from a secure location.
I'm surprised they don't exist already, to be honest