I am not quite sure exactly what you wish to do. I know it was commonly used with the Linksys series of ata's, however I believe I would drop using the # as a dialing indicator since the OBi uses the character to trigger other functions such as calling the other phone in the SPA202, and of course the # is used to signal the completion of entering other numbers such as Call Forward number. Using the # means that you would could impact other functions.
By default the OBi has a technique setup using **1xx. **2xx. **3xx. etc to direct calls to specific providers. Using the established techniques simplifies customizing.
If you have your Betamax account setup as SP1, without changing any default Digitmaps or Outbound Routing you can always send a call to SP1 by preceding dialing the number with **1. Your Betamax account will edit and reject a number that is not formatted correct. If you wish to make sure all dialed number got to your Betamax account start with 00 you could edit the default DigitMap for the applicable ITSP Profile setup for Betamax. For SpeedDials setup you can always send the SpeedDial to SP1 if you setup the SpeedDial with SP1 ... i.e. SP1(0044111222333)
For the calls going to atlasvoice, assuming you have it setup on SP2, just set SP2 Service as the Primary Line in your phone port. For SpeedDials setup your local numbers prefaced with SP2(xxxxxxxxxxx)