You guessed it! We have the technology to build floating cities, but lack the ability to communicate over long distances! Aaaah, fantasy, I love you.
Suppose you're the mayor of an autonomous city-state and you want to get a message to the mayor of a neighbouring city-state. You have a few options.
1. Smoke signals. Provided the weather is clear you can write your message in the sky. You're not limited to smoke, of course. Ground cities often communicate through a series of relays that might consist of rockets or mirrors. Downsides to this include the fact that such messages are easily intercepted, and relay routes are not always publicly available.
2. Mail Service. There are multiple mail services provided, but they're all slow and more or less unreliable. They're also notoriously untrustworthy--you never know when a mail ship will be boarded by pirates and the contents read or stolen!
3. Carrier Pigeons. Carrier pigeons are reliable, speedy, inexpensive, and trustworthy. Just make sure you feed them and hire a caretaker and all your messaging problems are solved. Everyone respects a carrier pigeon. If anyone started shooting them then everyone would start shooting them, and there has to be a line somewhere. Just don't try to send anything too long or bulky, like a mortgage contract!
4. And finally, the most common solution to the communication problem is couriers. There are many courier services and also freelancers. Couriers come in two varieties: local and long distance. Rates vary depending one what you want communicated, where you want it to go, and how dangerous it is. Couriers work indiscriminately for anyone, and generally can't be arrested for fulfilling their duties. Laws vary by region, of course, but a courier working for a pirate will tend to avoid those regions known to confiscate illegal goods. Couriers are also known to be sent on retrieval missions, making them bounty hunters of inanimate objects.