text messaging

Hey y’all! I need some help with programming some EF Johnson 5100’s. I’m having trouble figuring out how to set up text messaging on a conventional system. Any help would be much appreciated!

Our county is currently in the process of upgrading from an old vhf analog to a 700/800mhz p25 system. All the volunteer departments will be given unication g4 pagers. I have read where they are capable of doing text messages. Can someone explain that process to me