All future AMD products will support FreeSync but at present the technology isn't compatible with models that use cheaper display controllers. A list of AMD's GPUs and APUs compatible with FreeSync can be found over here.
FreeSync is based on an embedded DisplayPort capability that was formally added to version 1.2a of the standard spec. Like the rest of the standard—and unlike G-Sync—this "Adaptive-Sync" feature is royalty-free. There are some associated hardware requirements, but the additional cost should be minimal, according to Huddy, who told us he'd be surprised if FreeSync compatibility added more than $10-20 to a display's bill of materials. Even taking additional validation costs into consideration, monitor makers should be able to support adaptive refresh rates fairly cheaply. They're still free to charge whatever premium they want, though.Source: The Tech Report
There are no requirements surrounding the range of refresh rates that monitor makers must support. However, Huddy expects entry-level models to start at 24Hz, which is the most desirable update frequency for typical video. Higher-end implementations could scale up to 144Hz and beyond.