We had the chance of a good talk held by Olle E. Johansson, Edvina, the father of SIP channel in Asterisk. He provided a good overview of how OpenSER and Asterisk can be used together to provide feature rich VoIP service. Furthermore, he talked about Asterisk 1.4 and future plans for SIP.
Aside this a good remark was lack of good collaboration between major players in Open Source telephony. We all have to work on this, to collaborate to build an Open Telephony Platform. There will be no application that will achieve that alone. We should gather our knowledge and forces to make it possible.
I end with same topic as he did. Lot of people try to promote security as a big hole in VoIP versus PSTN. Next image from the slides is very much relevant (:-) in this respect: pstn-security.jpg.
Download slides of Asterisk Presentation