If I connect two cisco router 877 only wireless.can I telnet from one another without being connectedby cable?

toalymac is correct. The only thing I'd add is that you could (and in most situations today, would) configure AAA rather than hard-coding a local pword on the VTY lines. Either way, though, you would have to configure remote access before you'd be able to telnet to the router, wirelessly or otherwise.