I was unclear in my description of the setting, and since I can't attach a screenshot (that forum function is currently broken), I can't show you what I meant.
The "Primary Line for Outgoing Calls" setting does indeed control which Service Provider (SP1--SP4) is the default SP used when you pick up the phone and call. I led you astray with the fact that it will always refer to "Phone 1", which is the one and only phone jack used. So, what the setting truly means is: "If you pick up the telephone handset on the telephone plugged into the Phone 1 jack and make an outbound call, it will use this SPx." On a 202, it will show Phone 1 AND Phone 2, and allow you to designate two separate settings -- for example, use SP1 on Phone 1, and use SP2 on Phone 2. SP's and physical phone lines can be mixed up however you wish.
So: if you select SP2 as the Primary Line for Outgoing Calls, then your calls will be placed using SP2.
If you want to place the call using one of the other SPs, then you prefix the dial string with ** and the number of the SP you want to use. For example, if the default is to use SP2, but you want to use SP1, then press **1 followed by the telephone number.
The unrelated issue you are discussing is which Google account to save and use, and which Google account to use as your OBiTALK signin. Those two things are actually independent.
OBiTALK, the web portal, like most websites, is secured with a login. You can either create a dedicated username and password, having nothing to do with Google, or you can use an authentication service provided by Google, similar to the services provided by Facebook and Microsoft: You tell OBiTALK to ask Google who you are, and in order to do that, you sign into your Google account. It can be any Google account, independent of Google Voice. Remember: Google Voice is a service on a Google account. You have a Google account, not a Google Voice account. That Google account can be used to access any of Google's services, like Gmail, Calendar, Docs, etc.
So: you can use whichever Google account you wish, as your login credential, or, to avoid confusion, just create a dedicated signin directly with OBiTALK.
As for which Google account you keep or jettison, the reason I walked you through that procedure, was that most people have their Google Voice service associated with their "main" Google account -- the one they use for Gmail. So, I assumed your first Google account was the one you wanted to keep. It's all up to you; do whatever works best for you.