[nonameiguess]

I suppose there's no guarantee it'll work, but I just checked and you can apparently get an old vintage Motorola Razr on eBay for $10. They can just get phone numbers and text each other without needing to use a web platform. I'm guessing here the objection to a mobile phone is about unrestricted app and web usage and screen time, not just having a handheld communications device.

I'm tempted to say this would be less addictive than a smart phone, but thinking back to being a kid, my sister was almost always on the phone talking to her friends, so maybe not. But it at least restricts you to talking to people you already know and doesn't enable meeting arbitrary strangers.