Our phonebooth.net offers hosted voicemail transcription by email and you can read, listen, and manage voicemail from the web (as well as the phone, of course)

Our phonebooth.net offers hosted voicemail transcription by email and you can read, listen, and manage voicemail from the web (as well as the phone, of course). There is simultaneous and sequential group ringing. Conference bridging with up to 8 participants. Each user/phone number can also configure external phone numbers to forward to. Finally, you can create an unlimited number of "automated attendants" for your "press 2 to sound like a big business" scenarios. Along with nested menus to drill down to the right person/voicemail, if your needs are more complex. If hosted isn't for you and you are willing to get your hands dirty, try the open source FreePBX.org for on premise build out of the functionality you've described. Disclosure: I am on the phonebooth.net product team and are the primary contributors to FreePBX.