One thing that has always been at the top of the list on the mysipswitch and now sipsorcery feature request lists is the ability to initiate a callback from the dial plan by dialling in from a phone. The sequence of events would be:

1. Set up an incoming number that terminates in a sipsorcery dialplan,
2. Dial the number from any old phone, for example a work phone,
3. Once the call is received by the sipsorcery dialplan somehow allow a number to be entered,
4. Have the sipsorcery dialplan forward to the number entered in step 3.

Basically it’s a standard calling card gateway system but with the advantage for users of being able to forward the call through their sipsorcery dialplan to take advantage of whatever rules and providers they have set up.

The challenge for the sipsorcery service is that the feature will always require a media server for step 3. Previously a Blueface Asterisk server was configured for the task and it worked ok but it wasn’t ideal. Blueface need to look after their own customers and not get distracted with sipsorcery.

Lately I’ve been checking out VXML (Voice XML) providers to see if there is some way to hook up a VXML application to get the number. The advantage of VXML over an Asterisk server is speech recognition (Asterisk can do speech recognition to but it requires some serious hoop jumping). A VXML application will give users the choice of entering the number using speech or using DTMF. I found two companies that offer free or eval VXML sites and was able to progress with both. The two companies were TellMe and Voxeo. I was able to get to a state where I could create a VXML application to get the number from the user. The tricky part has been how to get that number back to sipsorcery. The best mechanism would be a SIP blind transfer which would use a REFER request to indicate the number the user had entered. Unfortunately I couldn’t get any kind if transfers to work with TellMe and Voxeo will only allow Attended Transfers on their evaluation platform. I contacted Voxeo support and explained that a SIP blind transfer means it will be even less work for their server but they have strict rules in place for PSTN blind transfers, which in fairness could cost them a bundle if not policed properly, and they don’t appear able to allow blind transfers only for SIP.

Voxeo do have an eval version of their Prophecy server which I could set up but I’m keen to avoid hosting a media server so I’m still looking around for a VXML provider that supports SIP blind transfers. If anyone knows of one I’d be very interested to hear about them.

Aaron

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