Need help solving (easy?) coding problem with inserting values

So, I'm trying to make a device with an arduino uno, an adafruit fona and a gps module.

The gps module will spam coordinates to the RX of the first arduino. These coordinates will be sent over to another arduino (which is hooked up to the fona). The goal is that if you send a text to the fona, it will send back coordinates.

My problem is: how do you insert a value (like the coordinates) into this piece of code from the fona?

if (!fona.sendSMS(callerIDbuffer, "COORDINATES"))

Thanks a lot (sorry if this is a noob question).

sprintf