Did you update to OS X Yosemite and some of the Continuity features are not working? This may be due to a poor/incorrect setup or due to the fact that you are running the new software on old hardware.
Sure you can buy a new Mac, but wouldn’t it be easier just to find ways to enable all the great stuff like handoff, SMS Relay and iPhone calling?
A team of developers lead by dokterdok managed to find a solution. They call it “Continuity Activation Lock” and you can download it for free on GitHub.
It will activate Continuity by checking compatibility and whitelisting the Mac board-id and it will give you suggestions when it comes to parts (hardware) updates. All you have to do is download it, run it and don’t be afraid to do all the requested commands in Terminal. They are pretty easy to follow.
By the way, my problem with iPhone calling still doesn’t work. On the other hand, SMS relay is working fine and I’m using it a lot.