I'm guessing your router changes IPs every day, because its an ISP with 24hour uptime and it gets cut off every day? (Mines like that, anyway..) If you can't influence the router to send you a mail or use a dynodns.net type thing, then thats a little difficult.. Or can you get the router to send a mail? (Mine does a ifconfig | mail my@work.address -s IP in it's ip-up.local)
For telnetting to the router and using that text-menu (from inside the network) you might be able to use Net::Telnet and Expect ..

C.