Suppose you want your contacts in Singapore and Canada to be able to reach you with a local call; there are several options. They could dial a local iNum or SIPBroker access number, followed by your iNum or enum. With many providers, that would be free for you, but if your only connection is via Ooma, you'd have to pay someone to forward the call to your US Ooma number. Likewise, if you got a dedicated number in some country, the incoming calls would likely be free to a VoIP connection, but there would be a charge to send them to Ooma. One free solution for your present setup is Rebtel, though it requires you to make a callback on each incoming call.
Many folks use the OBi110 with pseudo-landlines, i.e. locked VoIP devices with no direct IP access. Cable "digital phone" and Vonage are typical examples. If you don't foresee such a service or a landline in your future, the 110 offers no benefit.
Say you're in Singapore and using a Singtel prepaid SIM. If you are spending (for local outbound) at least SG$20 per 20 days, you'll have unlimited free incoming. You set up your OBi back in the States, so that when you call it, it doesn't answer and calls you back. Through the AA, you can then make an outgoing call. For example, if calling the US pr Canada, using Voxbeam Premium for the Obi->SG leg, and Google Voice for the outbound leg, the cost is only US$0.0075/min. If you're running e.g. 30 minutes per day, the total (including mobile service) works out to only US$0.033/min. And, quality is likely better than Singtel's budget 019 service (US$0.124/min. days, $0.062/min. nights and weekends).