i think for giga, you can "port-in later" to replace your current number. Means, you can subscribe giga with a new number, you can so-called try for a month, then apply for port-in to replace your new number with your current Orange telco number. Then you retain your old number.
I would suggest you try it out giga first with the $10 plan. I've tried giga before, not really impressed with it, and switched back to orange camp. But I switched to SIMBA afterward. Orange is pretty good in most places, but even with reception, data is slow. Giga is no reception or got reception, cannot receive calls.