Welcome to the forum
If everything is at default, then I would expect all calls to be going out on sp1 as this is the Primary Line. Dialling **2 followed by a number will force that call onto sp2.
Both sp1 and sp2 have a default DigitMap of:
(1xxxxxxxxxx|<1>[2-9]xxxxxxxxx |011xx.|xx.)
The xx. rule is a "catch-all" meaning any number of any digits. This means that all calls should be going out, if your Service Provider accepts the call format. There is a long delay of 10 seconds if the xx. rule is being used as it waits to see if you have finished dialling.
Are you sure that both Service Providers are showing as registered? (Click on your Obi number in Dashboard to see.)
To see where the calls are going have a look in Call History. This can be accessed by looking at the web page of your Obi – dial ***1 for the ip address. Then go to Status > Call History. This will show the last 200 calls.
When we have the basics working, then we can come up with some slick DigitMaps to speed up dialling and remove any need for ** codes.