How to Use SIP to Make Google Voice Calls
Integrating SIP with Google Voice
Google Voice provides the functionality to forward all incoming calls to a telephone number. You can also forward them to your local Google talk application thereby allowing you to make and receive calls within Gmail. It's unfortunate however that it doesn't allow forwarding to SIP addresses. Whether this is an accidental omission, or a deliberate decision so as to not upset the telecom carriers on whom Google relies to further its Android operating system, is a matter of debate. However, with a little bit of clever configuration, we can integrate Google Voice with an existing SIP service for incoming calls. Outgoing calls are still a little bit of a problem however. At least if you want to use the same Google Voice number as your identity.
To start with, you need a US telephone number that is linked to an SIP address. If you already have update SIP service, this number should be available to you automatically. It's the same number that people call you when you're using your VoIP service. If you enter this number as one of the forwarding telephone addresses in your Google Voice settings, you will find that any incoming call is routed to it. But if you don't have a paid SIP service and merely have an existing SIP address instead, you need to go through a few more steps.
Signing up with an SIP Provider
There are many free and paid SIP services available. If you're not looking for a professional VoIP system, you can sign up with any number of SIP PBX providers who will give you an SIP account for free. If you want a telephone number to go along with it, you probably have to upgrade to a paid plan. As mentioned before, Google Voice does not provide the ability to forward calls to an SIP address. Fortunately, a service known as IPKall gives you a free US telephone number that allows you to forward calls to a VoIP service.
So you need to sign up with IPKall, and then input the telephone number you receive into your Google Voice forwarding settings page. In the IPKall configuration screen, you need to input your SIP address in turn. So when you receive an incoming call from your Google voice number, it goes to IPKall who then sends it to your VoIP provider. It may seem a bit of a roundabout way of doing things, but until Google Voice provides the ability to forward directly to an SIP address, this is what we have to do if you don't have a paid US telephone number linked to a VoIP service already.
Of course, none of this will be sufficient for a business. You will need professional hosted VoIP systems to take care of your organization's requirements. Find out how you can get started today in less than 15 min.