I might be mistaken, so please correct me if I am wrong, but are these credentials of an account from the hosted PBX service offered by OnSIP? Are you sure you wish to interconnect two hosted PBX services? Will there be any particular advantage from their interconnection?
If indeed there is, you should use these credentials to establish a Trunk on your PBXes account. But if the OnSIP Proxy requires specifying both the Username and the Auth Username, you won't be able to set it up as the holder of a SoHo account.
thanks for reply, i am trying to use sip@natures.in as inward sip uri. onsip provides this facility, i have configured my voip devises on pbxes.org and i would like to set onsip hosted account as trunk.
if you could suggest any other idea then please suggest, does pbxes.org provide this functionality.
On another note, if the sip@natures.in can be changed to natures-SomeText@natures.in you might be able to accept the inbound calls via a corresponding Inbound Route in your PBXes account.
On a completely different note, if you can make changes to the DNS Records of your domain, then you can add the proper SRV records to accept inbound SIP calls directly on PBXes, without having OnSIP to act as an intermediary.