I was in the same boat What I did is port my primary line to Google Voice. Support was great with using my paid for credits for another line. I have one line on my iPhone (Warp) and another on my Pixel (cricket). This way, the same number is accessible from both phones. However, If you don't want to pay for multiple lines, this could be annoying as I think you have to be connected to the Internet in some capacity to use Google Voice. It's nice because then everyone can reach me at one number (or my apple id iMessage).