Hi Mandy :-)
For the last two years or so, since I got a better calling plan, we've primarily used cell phones in the parks with mostly good success. But for about six or seven years before that we primarily used 2-way radios (also known as walkie/talkies in the parks). Ours were similar to the Motorola T5000 Talkabouts. If you go on Amazon.com and search for "Motorola 2-way radio" and you'll come up with many choices ranging in price from about $30 up to about $100. Most of the radios have a two or five mile communication distance, which works perfectly within a theme park or resort, but it is not effective for communication between parks or resorts.
Basically what happens is that you have a pair of radios. You set them both to the same radio frequency channel. When you want to talk, you press a button, and the other radio beeps. Then they "pick up" your page and can talk to you.
Once you pay for the radios, you're done with the expenses; there are no additional charges to talk as much as you want. I'd say that about 90% of the time the radios were an effective method of in-park communication. I do have a few cavets about the radios, which I discussed in the question
HERE.