I'm not sure quite what you are looking for here. Prefixing calls with **3 and **4 will enable you to make calls through those respective service providers.
Trunk Groups is quite an advanced OBi subject and may be more than you want just now.
Lastly is there any good reason to configure the device locally as opposed to using the web portal. If these questions are self apparent I apologize but find myself just scratching my head.
Sounds like a simple question, but not so! This question is so contentious that the argument raged long in the early days between highly respected users such as RonR and MichiganTelephone. Sadly, as a result, they both left this forum. See some of the issues here:
http://www.obitalk.com/forum/index.php?topic=2932.msg19408#msg19408For what it's worth, my opinion is to stay with the Obihai recommended web portal at least until you have looked at the pros and cons in some depth. Sorry I can't give a more simple answer!