You don’t need to call your phone company. (They almost certainly have nothing to tell you, and do not need any information from you to resolve this.)

All you need to do is ignore the sms and forget about it.

So this spreads further than just the local island?

Your computer may well still be infected. Any number of trojans may have been installed, so even if one was found and removed by your virus software, that’s not much of an assurance. You could try another virus package, and also run RootkitRevealer to see if it turns anything up. But even then you can’t be sure.

It’s also possible that there’s nothing there. Windows often does a fine job of slowing down and getting unstable by itself, without any help from viruses.

The only real way of knowing is by saving your data somewhere else, formatting your hard disk, setting up Windows from scratch, and fetching your data back. And hope none of your Word documents got infected … I believe that’s less common nowadays anyway.

That’s as sure as you can get, but that costs plenty of time and hair. (A common workaround is to make it somebody else’s time and hair, which tends to cost either money or a friendship.)