I just finished working with a consulting firm to implement a cisco cube router so that we can do calls with our other companies that aren't on our network.
We tested with offices all over the world and we could call them and they could call us. But when one of the companies trys to call another one of our locations on our network they get a busy signal. I've talked to the firm that helped me set this up and they said that it's something on there lync server they need to modify because they have only one route to us and not any of our other locations. I just wanted to make sure that they are telling me right and that there isn't something that I need to do on my end.
Based on the info you've given they could be correct.
For instance, if your site has an extension range of 6000-6999 they may have a dial peer for 6XXX pointing to your cube router.
If your other sites have different extension ranges, 8XXX ,5XXX, etc. Then the Lync server would need the appropriate dial peers to forward those calls to the cube for proper routing to your other remote sites.