@Oddbloke: Oops. Was looking at my SVN WC, so, yeah, got the wrong L° ;D.
Yeah, I indeed meant the iptables line

.
Something in the vein of
Code:
iptables -A INPUT -i wlan0 -p tcp --dport telnet -j ACCEPT
should do the trick. (+ UDP if needed, I'm not familiar with the inner workings of the telnet protocol and can't remember how much of UDP is blocked by the default rules.)