Would like some advice from the Debian VoIP maintainers about sustainable Debian sip server

[Jelle de Jong]

I am searching for some starters information, I build small Debian 
servers for medium sized companies with 2 up-to 100 people and I would 
love to add sustainable sip functionality.

I am searching for the following like to have features:

OpenLDAP or vCard contact book provisioning
Possibility to redirect a call to other (SIP) telephones
Logs of outgoing and incoming calls and telephone id's
Digital voicemail to email
Registrar on sip server and when dialed all phones ring and can answer
ENUM technology capable or upcoming
All GPL compliant Free/Libre Open Source software

Like to have project management features:

Free (as in speech) documentation for setting up a Debian server
Growing community with a core that are volunteers
Debian packages with maintainers that responds to bug reports/mails
Community where companies are welcome to give support with SLA's
People for patch reviewing and inclusion in upstream

What are my options for tomorrow and what looks good for over a year?
What would be wise to invest time, energy and money in?

http://en.wikipedia.org/wiki/List_of_SIP_software#Free_and_open_source

What would you recommend and how to proceed?

Thanks in advance,

Jelle de Jong