Cheogram is a way to connect any device with an Internet connection to the telephone network.
Jabber is a way for computers to talk to each other and enable things like chat, voice and video calls, and more. A JabberID (JID) is your address for use with anything that speaks Jabber, including Cheogram. You can get one here.
Once you have a JID, you'll need a program that speaks Jabber to use Cheogram. No matter where you got your JID, you can use any program that speaks Jabber and it will work.
Cheogram assigns every phone number in the world a JabberID so that you can communicate with telephones using Jabber software. Sending a message to +email@example.com would send SMS to that phone number, for example.
To work properly, Cheogram has to be connected to a "route" that will give you a phone number. Not every route supports the same features, but our goal is to make them as similar as possible. You can try one free for 30 days by clicking one of the phone numbers on the Cheogram homepage and signing up.
Check out the FAQ for XMPP users or the Soprani.ca wiki.