I have an IAX trunk up to my service provider, plus a Linksys SPA3000 SIP ATA and an IAX softphone (Loudhush) on the Macbook. Call quality over ADSL is far better than analog voice or cellphones.
Just one gotcha when upgrading from the previous release: the IAX trunk appeared to connect but didn't pass calls through. This turns out to be due to a new security feature in recent Asterisk releases. To fix this, login to the HTTP GUI and enter some manual attributes:-
AdvancedIf your firewall doesn't block access to 4569/udp from untrusted networks, you probably want to read up on how to secure these settings properly.