I don't understand why you don't get the correct CID. Like I said, mine works.
Anyway, you can try the following.
Get a free Sip2Sip account here:https://mdns.sipthor.net/register_sip_account.phtml
On OBi2 register one of the SP trunks to your Sip2Sip account.
Service Provider -> ITSP Profile A or B -> SIP
X_DnsSrvAutoPrefix: Enabled (checked)
Voice Services -> SP1/2 Service
Change Line Port -> InboundCallRoute to: