We have issues with this type of set up before, please see below an extract from a conversation I had with a high level system engineer at Afrihost. I have had a few clients try this method with success.
I have replicated this problem using the DLINK router and zoiper (SIP client) on android. The problem does NOT appear on the DLINK router and media5 (SIP client) on android.
The error you reported is the text I see on Zoiper on android (503). The problem was visible behind the DLINK, and not from the network the DLINK is plugged into. It is not possible to use the DLINK without "SIP ALG" enabled, which I believe is default. The connection to sip1.freshphone.co.za does not attempt to pass through the router - for reasons I cannot establish.
The problem does NOT appear for me when changing the host name from sip1.freshphone.co.za to the IP address 188.8.131.52
The problem does NOT appear for me when changing the host name from "sip1.freshphone.co.za" to "sip1.freshphone.co.za:5060"
Taken together, this means that the DLINK SIP algorithm is unable to handle the host name unless it has the port number appended."
Please give it a go and see if it works better for you.
I believe so, since you are using a DLINK and on the afrihost network, I think you are the perfect candidate for this solution, please let me know if it works or doesnt work for you.
It would seem, from Afrihosts reply that the router requires SIP ALG to be enabled, but you also need to append the register server with the port number :5060
I guess that its a requirement on DLINK, maybe they did not adhere to RFC standards, Im not sure.
With regards to other ISP's, I think some do yes, I know we have huge issues with CellC. I think this is more related to the router than the ISP, I seem to remember a client changing their DLINK to another router and using afrihost fine.
Safe to assume the issue is resolved?
Awesome, its a pleasure.