I'm very surprised that this is happening. This typically occurs when the caller is using an IP or ISDN phone, and forwarding occurs at the provider level, or the call is transferred with a REFER request. It would be possible from a cell phone, but I'm not aware of any wireless carrier that propagates redirect info. From a landline, it's impossible, even in theory. So, I'm very curious about the specifics: What kind of phone is caller using? Who is his carrier? Your SIP DID provider? Provider used for the forwarding?
In any case, confirm that you are not doing forwarding or "follow me" at the DID provider. Also, confirm that X_UseRefer is off in the OBi, which is the default. If the caller is still seeing the redirect, there is IMO a bug in the OBi firmware. Use SIP Debug to see how your number is being leaked.
Thanks for your reply.
Wow, you are right. I looked into and found out that the problem is only evident when someone makes a call using SIP phone not using landline or cellphone.
One quick question: where can I find X_UseRefer?