partially solved the problem.
1) the spa-3102 firmare was outdated - updated it to 5.1.7 (5.1.10, the latest, have bugs, according linksys community list)
2) i was connecting the spa-3102 to the network via LAN port - does not work (but the wikis does not point this detail out - so i updated one of them). Connection via WAN port worked.
Partially solved because there is still a strange problem:
- calling from outside to the house line and picking up the call - when hangup, line free - that's the right behavior.
- calling from house line to outside and call picked up - when hangup, line free - that's the right behavior.
- calling from outside to house line and NOT picking up (call dropped) - line hangs - that's the WRONG behavior.
Did try to change the disconnect tone pattern, to accomplish brazilian standards, but did not work.
It seams that asterisk makes the voice prompt, and do not hang the line after called number disconnect.
Does anyone faced this problem before and may help?
Unfortunatelly, i'm too new to asterisk (started just one week ago to handle with it).