I'm trying to get a better sense of how dual eSim functionality works when traveling, in particular with an iPhone.

Let's say I'm a U.S. citizen and Verizon customer who is going to be spending a couple months in Singapore. I can activate my second eSim with the relevant provider in Singapore, and that way can ensure coverage in Singapore. That part seems straightforward enough.

But what if I also want continued access to my Verizon number while in Singapore, in particular so that I'm able to check my text messages (both iMessage and SMS) and to receive security codes that are texted to me (which generally come via SMS).

How can I maintain access to my Verizon number in this manner without constantly paying for Verizon Travel Pass days, which would quickly add up over the course of two months?

(Also, how exactly does eSim work? Are both numbers active at the same time, or do I have to manually switch from one to the other depending on which number I want to be using?)