// Should match a phone number
/^(()?d{3}())?(-|s)?d{3}(-|s)d{4}$/

var string = "555-790-2342 is one, 555-555-2344 is another.";

var numbers = {
    "555-790-2342" : "John Smith",
    "555-555-2344" : "Bob Smith",
    "555-324-2342" : "Dana Smith"
};

string.replace(/your regex here/g,function(match,sub1,sub2) {
    // for obvious reasons, use meaningful argument names!
    // now do stuff
    // optionally:
    return match;
});