Will my smartphone work for Sip trunk?


Jul 18, 2016
My company is going to switch their communication network to Skype hosted pbx. They have subscribed to sip trunking for Skype for business. I don't know if my smart phone is compatible for sip trunking. It's an old model from Microsoft, Lumia 920, 1GB RAM. do you think this feature works on it? Will I have to buy a new smartphone?

The Lurker

[H]F Junkie
Jul 1, 2001
Why not ask your companies cellular department and tell them to give you an approved phone?


[H]F Junkie
Oct 23, 2000
TL;DR: Install the Skype for Business client on your phone.

If your company is using Skype for Business, they're trying to abstract the SIP trunks away from the end-users. You'll be logging in to Skype for Business using your Active Directory account, and the Skype for Business Front-End server will establish inbound/outbound connections to your SIP provider on your behalf. Therefore, it doesn't matter if your Lumia 920 is capable of connecting to a SIP trunk directly -- it can connect using the Skype for Business client written for Windows Phone 8/8.1/10. I haven't used a Microsoft phone, ever. However, I have used the Lync 2013 and Skype for Business 2015 client on my Nexus 6, and there are three call handling options ("Voice Settings" in the client settings):
  1. VoIP Always. If you're making a call via Skype for Business, your phone will establish a TCP connection wtih the Skype for Business server, and will make a VoIP call the same way your desktop Skype for Business client would. This option forces VoIP over LTE or Wi-Fi, depending on what you're using at the time.
  2. VoIP over Wi-Fi only. If you're connected to Wi-Fi, Skype for Business will make the call over VoIP. Otherwise, it will fall back to Cellular.
  3. Cellular. Calls will come in to your phone over GSM to the number you have specified in the Skype for Business client settings.
Additional note on the Cellular setting: if the Skype for Business server receives an inbound call to your assigned SIP trunk, it will simply forward the call to your cell phone. This is pretty much the same as setting up call forwarding on your desktop Skype for Business client. Outbound calls also work -- your phone's Skype for Business client tells the server which number you'd wish to dial, and then the server dials that number and your cell number. This means that an outbound call using the Cellular method is actually an inbound call to your phone ... but I digress :)

Note: all of this assumes that your company is running Skype for Business on-premises and has configured the relevant front-end, back-end, edge, and reverse proxy servers correctly. The company I work for has run Lync 2010, 2013, and Skype for Business 2015 on-premises, and I've installed/configured the various server roles (including the reverse proxy on Microsoft TMG, Microsoft IIS ARR, and Kemp LoadMaster devices) on the 2013 and 2015 versions myself. If they're not exposing the Skype for Business servers to external users correctly (or intentionally), you'd likely need to connect to your company's VPN from the phone in order to use Skype for Business correctly. Also note that inbound calls to your phone can be set up from the Skype for Business desktop client by configuring call forwarding, and that this method does not require you to install anything on your phone.

Hope this helps :)