There should be no serious problems forwarding incoming GV calls to your mobile.
One minor issue is that your mobile would show your landline number, rather than the number of the original caller. The only fix is forwarding via a VoIP provider, which would likely be considerably more expensive.
If the landline is in use, either locally or for another forwarded call, the caller would get GV voicemail. To fix that, you'd have to either get a second OBi110, or route the second call via a (likely expensive) VoIP provider.
For forwarding outbound calls from your mobile, I can't be sure that the OBi will be able to recognize your mobile's caller ID. Perhaps a member with an OBi in UAE can answer that. If caller ID does not get recognized, you can either have the autoattendant answer all landline calls (regular callers would have to press 1 to ring through to your landline phone), or you could have the AA pick up after a delay of e.g. 15 seconds. The latter approach would not be good, if your wife or kids are at home when you'll be calling, as they'll be needlessly disturbed.
As I previously requested, please post the costs of calling to and from mobiles within the UAE. That will be useful to other readers, so they can intelligently choose among various approaches.