Holisticware ofers installations and support like maintenace for Asterisk Server and diverse application suites based on Asterisk like: TrixBox, AsteriskNow etc.
For those in doubt also offers VoIP consulting.
Development of office applications for VoIP.
Detailed References
Asterisk FeatureCodes Shortkeys cheat sheet
Asterisk and derivatives 2N GSM gateway setup
Asterisk and derivatives Portech 37X GSM gateway setup