How to send messages from a phone without the internet
What an Android phone can still do without mobile data: Bluetooth, Wi-Fi Direct, a local mesh and the role of offChat.
Direct answer
Yes: two nearby phones can exchange notes without mobile data and without router Wi-Fi if they use a local radio — Bluetooth or Wi-Fi Direct — and the same compatible app on both sides.
This does not replace WhatsApp, SMS or a call to someone in another city. Without radio proximity there is no delivery.
What the phone can still do when the carrier vanishes
Cellular (4G/5G) and access-point Wi-Fi are only two ways onto the internet. The device still has Bluetooth and, on many Androids, Wi-Fi Direct: phone-to-phone links.
A proximity app uses those radios to discover who is nearby and send text. The internet can stay off.
Where offChat fits
offChat is the local communication module of the KingFy Android app. Both sides need that app open, with radio permissions granted.
We do not invent kilometre-scale range. Walls, crowds and terrain shrink the link. A mesh chain only exists if intermediate phones also have the module on.