When you turn on GBP call tracking, it simply defaults to the first GHL number you purchased and swaps that out for your primary number on your GBP account. However, if you go to manage channels, you can put any number you choose from your GHL numbers under text messaging and that will act as your GBP tracking number. It's not intuitive the way it is now, and if you don't know, you'll never figure it out. What would be ideal is if when you turn on call tracking for GBP, it simply asks you via a drop-down where the displayed number is now as to which number you want to use.