sms <scharf.steven@geemail.com> asked
> receiving SMS in Airplane Mode is not possible

It might be possible if the carrier supports SMS/MMS on Wi-Fi calling.

Mine does (T-Mobile, USA), where the test I ran was simple:
a. Turn off all radios via Airplane Mode
b. Turn on _only_ the WiFi radio
c. Also turn on Wi-Fi calling

In my test, I was able to send MMS/SMS texts with Wi-Fi calling turned on.
It was unable to send MMS/SMS texts with Wi-Fi calling turned off.

REFERENCE:
<https://home.pulsesms.app/help/>
Q: Can I text when I have a Wi-Fi connection?
(or do I need a connection to my carrier?)
A: At its core, Pulse SMS is just an normal SMS app.
If you have no signal on your phone (zero bars), the app will not be
able to send messages, regardless of what device you are trying to send
from.

There is one exception to this, but your personal usage may vary.

Some carriers have WiFi Calling that you can enable/disable at the system
level. With some devices and carriers, enabling this will allow you to
send messages over WiFi alone. You will need to test this for yourself,
to see if this functionality works in your situation. I am not able to
provide a complete list of carriers or devices that this will work on.