[borgel]

Punkt MP02 might meet your needs. https://www.punkt.ch/en/products/mp02-4g-mobile-phone/

[SoftTalker]

I like the idea but that's a lot of money for very limited features. I understand the lack of features is the point, but a Nokia 6300 4G KaiOS phone is only $70. No Signal, but it has WhatsApp.