Hooking up phones in remote offices via SIP

I’m a noob so take it easy on me, I may not explain this correctly.

I have built an AsteriskNOW system with FreePBX GUI for our office. I am running into an issue setting up remote phones at satellite offices via SIP. I WAS able to hook up a softphone (Voiper) on my Android via IAX.

Can phones be connected remotely via SIP? What do I need to do to my AsteriskNOW server and/or Router to make that happen?

I have spent about a day reading numerous threads on the subject and they are either over my head, didn’t apply to me, or didn’t work.