Lilygo T-Beam 

 sorry wrong answer
i use it to send and receive messages
over 915 MHz Frequenzy 
so i need no internet or wlan 

 Next, you should probably try sending some Bitcoin, haha! 

 That's what i thinking. You can send bitcoin transaction ? But it's only validated when you back online ? 

 Well, I'm not really sure either because I haven't tried it yet. 

 Interesting