LoRaWAN is not build for sending txt messages in general, you probably get in trouble with the fair use policy very fast imho , I assume you want conformation that your message(s) arrived ?
Another problem I forsee is the max payload size, bigger message means splitting it up and waiting in between the message parts to comply.
And the devices are presumably mobile, what if the device receives only first part and not the second, So no conformation the message is complete ?
LoRaWAN data rate and application packet sizes :
The data rate and maximum packet size roughly depend on the distance to the nearest gateway and the type of data to be sent, and are also defined in the specification for each region. Like for the European
863-870MHz band, the application packet size varies between 51 bytes for the slowest data rate, and 222 bytes for faster rates. Note that the LoRaWAN protocol adds at least 13 bytes 121 to the application payload. And beware:
Some libraries, such as LMiC 70, only support 51 bytes for all SF.
Some providers, such as the Dutch KPN 32, only support 51 bytes for all SF.
- Limitations: data rate, packet size, 30 seconds uplink and 10 messages downlink per day Fair Access Policy
- duty cycle for LoRaWAN devices
- Limitations of LoRaWAN
Technically they can be build on a LoRaWAN network … but I think you must see them as emergency devices only, not for daily use to send messages to your friends.