Can I turn off an eSIM I'm not currently using (ie. have dual SIM: US carrier SIM, and Spain ES carrier SIM)

You can toggle on/off either (or both) of your lines at:

Settings -> Mobile -> eSIM

This doesn’t affect your SIM(eSIM) it’ll be ready for you to turn it back on.

Hi rg357,

Thanks for posting here in Apple Support Communities. If you're no longer using an eSIM, it can be erased or kept. You can see more about removing the eSIM here: How to erase the eSIM on your iPhone - Apple Support

You'll want to reach out to your carrier for specific details on how you're texting or roaming will work. Take a look at this as well: About eSIM on iPhone - Apple Support

rg357,

As noted in the following resource, you may need to contact your carrier:

About cellular data roaming options for your iPhone and iPad

Turn off Data Roaming or prepare for a trip

Need to avoid roaming charges because you arrived at your destination without an international data plan? Check your Cellular Data options and turn off Data Roaming.

1. In the Settings app, tap Cellular, or Cellular Data, or Mobile Data.

2. Turn on Cellular Data, then tap Cellular Data Options.

3. Turn off Data Roaming.1,2

Still planning your trip? Here are three other ways to prepare:

Shop roaming plans with your carrier

Before you go: To avoid fees and higher rates, contact your carrier by phone or online to shop international roaming plans.

After arrival: Open Settings. Tap Cellular, or Cellular Data, or Mobile Data. Then tap Cellular Data Options and turn on Data Roaming and other settings suggested by your carrier.

Shop roaming plans with eSIM

Before you go: If you have an iPad with an eSIM, you can browse cellular data plans from select carriers in more than 90 countries, regions, and territories.

After arrival: Go to Settings > Cellular Data and buy a roaming plan that fits your needs.

Beginning October 1, 2022, Apple SIM technology will no longer be available for activating new cellular data plans on iPad. If you're not sure if your iPad uses Apple SIM, find your iPad model and click the link for its tech specs.

Hope this helps!

Have a great day.

You’re welcome.

Have a GREAT trip!