Do I need an additional SP?

[azrobert]

I always use Port Range Forwarding.
If you're only doing one port then the start and end port will be the same.

[noobee]

Even after port forwarding I am not able to call to my SIP URI using flapphone.

[giqcass]

If you type 192.168.1.102 in your web browser do you get a prompt for a password?  Something similar to the following.

A username and password are being requested by http://192.168.1.102. The site says: "user@OBi100"

[noobee]

I haven't tried that, but when I configured SIPGATE on my SP2 and tried calling from flapphone, it worked, I received call on my Obi, but there was no audio both sides.

When I set up DID forwarding on Callcentric, the call was not forwarded.  There's something wrong with the DID forwarding on Callcentric, and there something wrong with the SIP URI Audio.