I am writing some software to support a sip complaint device. I am having some issues testing the REFER Message. The 3cx PBX eats the command and it never gets forwarded to the product.
So what I need is a SIP phone that will allow me to transfer a call directly to an IP address. So I want to make a Direct-IP-Call to the SIP Phone, then transfer the call to another SIP Phone via and IP address. The grandstream phones that we have only allow transfers to extension numbers not IP addresses. These phones won't even allow us to put an IP address in a person's contact info.
Can someone recommend a SIP Phone that will do this feature?