Indu Kodukula has an interesting presentation posted on the BEA World site. The title is "WebLogic Communication Platform Overview". It actually has good highlights on the IP Convergence market itself. For example it says that the largest consumer VoIP operator in the US is built completely on the Web Logic SIP Server (hint: Vonage?). Overall 30% of the US operators are ready to do a one time sweep migration to IP Communications. This is pretty significant number in terms of market size.
70% of the US telco operators are not ready to dump their investments in legacy Intelligent Networks. The percentage in Europe is even higher. Most operators need a platform that will allow them to integrate legacy stacks such as SS7 with IP protocols like SIP.
This further helps explain the positioning of SIP Servlets vs JSLEE. The former standard is the right choice for the operators that are ready to make the sudden switch, while JSLEE will be important for heterogenous environments.
Another bit of interesting information in the presentation is that Web Logic SIP Server 2.0 does not have Session Replication and Clustering implemented yet. These features are scheduled for a new release later this year.
I can't help to mention that Mobicents already has clustering capabilities and demonstrated SIP failover at VON last week.