D-Link DSL-2640B and Voip/SIP

Are you using a D-Link DSL-2640B adsl modem/router/switch/ap and VoIP/SIP applications are not working (like, you place a call, but you can only receive, or vice-versa, and some codecs are not even loaded).

Well, consider a firware upgrade: 3.xx software has a broken SIP Application Level Gateway. And upgrade with Internet Explorer, since Firefox/Chrome/Safari upload is broken as well. What do I have to do to get reliable connectivity at home? Buy a Cisco 1841? Find a DD-Wrt compatible router?