Cloud PBX with AA. What are the required add-ins?

Regular Contributor

This is a basic question regarding requirements for Cloud PBX with AA functionality.


I have a client that is 100% in the cloud, already running Office 365 E3, working in a virtual office environment (workers scattered about the country working from home offices). We're looking into SfB and Cloud PBX, but I can't figure out exactly the breakdown of add-ons required to do what they want.


Workers in this company need to take incoming calls from a main PSTN number via an auto-attendant. In other words, we'll port their existing main telephone number to Skype for Business PSTN as a Service number, and assign it to the auto-attendant. The menu choices on the AA should connect to specific individuals within the company, each of whom will be running Skype client on the desktop.


What I'm not clear on is that since they only need to answer Skype calls routed from the AA (and receive voicemail), and workers do not need to place calls to the PSTN, what is the right add-on for each worker? Do they each need Cloud PBX add-on only? Or do they also need SfB PSTN? (Yes that's right, you guessed correctly, I am a complete telephony newbie)


Thanks for any info,


9 Replies

Hi Bob,


This is my  understanding, but sure someone will be along soon to correct me if I'm wrong.


Your users will require 2 licences,


1) Cloud PBX licence, which essentially gives S4B the ability to have voicemail and receive calls. 

2) a PSTN Calling plan licence, which will allow you to assign the user a particular PSTN number.


Currently, O365 doesn't offer cloud-based hunt groups, although it's something which is currently in preview.


For your situation, the only thing I can think to recommend would be to give your users the required licences so they have a PSTN number and voicemail, then port your main service number into a third party cloud service, then setup the group to direct the calls to the users PSTN. I'm pretty sure RingCentral offer something like this.


On a side note though, be careful your users won't exceed the allocated PSTN minutes, otherwise you'll need to setup PSTN consumption also.


Hope this helps

Thanks for the reply, Steve.


So are you saying that *each* user will require both a Cloud PBX license *and* a PSTN license? The latter requirement is what I don't understand - I guess in the old-school world of on-prem PBX's we'd have, for the sake of argument:


1) A single (or more) "outside" lines from the phone co (only as many needed to support the # of expected simultaneous calls with the outside).

2) An auto-attendant, and bunch of extensions inside, as implemented by the PBX


I guess I don't understand why each and every user must have a PSTN license, and in particular if we want dedicated Skype accounts that are really just there to receive voicemail only, but never place PSTN calls. From my limited playing around with a test tenant, it also seems that I cannot enable voicemail for a Skype user unless it has both Cloud PBX *and* PSTN - just Cloud PBX for a Skype user doesn't seem to give that user voicemail.




Something to note for your scenario is that extensions are not supported currently so everyone will have a full 10 digit number (I am not sure you could block someone from direct dialing them if that was something you wanted to do).

Also AutoAttendent is currently in Preview and is extremley basic at the moment.



Hi Bob,

Thats correct, each user will need a Cloud PBX and a PSTN Calling licence.

The PBX licence does light up the voicemail feature in Skype for Business, but without a PSTN number assigned, they would only be able to receive calls and take voicemails from other Skype users as a Skype > Skype call.

The PSTN licence is what gives you the ability to add a PSTN number (inbound and outbound) to the user, which would then roll to voicemail is unanswered.
Thank you Steve, however, this is part of my confusion. For those users who've been assigned PBX licenses (without PSTN calling), they do not seem to have any voicemail capability whatsoever. There are no settings that light up, and Skype to Skype calls to these users never go to any voicemail.

Strange, have you checked to see if they have Unified Messaging enabled on their mailbox under the Phone and Voice Features?



Also, when the have a PBX Licence assigned, if they sign into S4B, they should also see the telephone dial pad as a new option.

I don't belive you get voicemail until they have been assigned a phone number (And you need the PSTN addon for that)

I have tried flipping it on and off globally and for individual users and it makes no difference - the extra dial pad (and vm settings) tab never appears in SfB client for users unless they *also* have a PSTN license assigned. Furthermore, I have found that I can leave UM completely disabled for all users and users with PSTN still have full voicemail capability (but those with Cloud PBX only do not).