The TNC contains all the software and special hardware that you need. This is just as easy as connecting your computer to a modem. If you don't want to use the serial port of your computer, there are TNCs available that will plug directly into the bus. If you can plug an RS-232 cable into a modem, and wire the TNC to your radio, then you have all the ability that you need. I am sure that there are hams in your area who would be glad to help you if you are not comfortable with wiring a microphone connector.
Installation really is very simple, and once it is done, there is virtually no maintenance.
If you like, build a simple switch box to allow easy changing between your TNC and voice operation. I don't recommend it, but some people wire the TNC and microphone in parallel, so that they don't need to change the plugs, or switch anything at all. I believe that packet radio is still in its infancy. Of course, this is limited by the amateur radio rules and regulations, so there cannot be any commercial messages. Here in New England we have connectivity over most of the region.