The receiver that has sling built in is called the 722s (not he model 722) and DISH is changing the name to ViP922 so people don't get it confused with the 722. DISH has not said when it will be released.
If you want to sling programs from your 722 you will need to buy a (separate) Sling Box.
If you want to sling programs from your 722 you will need to buy a (separate) Sling Box.