Converting junk and Eagles into cell phones

I have a nice size collection of junk dimes,quarters, and half dollars. I also have silver eagles. Can these be legally melted down to use the silver in computers and cell phones. I am talking about a future when and if we have very little silver left. I was recently told that melting down any government minted coins is illegal. So if you want to save silver for this reason you should save only bars and rounds. Can anyone fill me in on the real story about this?