True, 128kbps wasn't anything that'd compare with 4G, but this was 1999. It wasn't great at handoffs either, but still, I was able to use it on BART regardless. Imagine, connected to the net - on the move!
It's certainly possible to build a 900MHz mesh network, but it can't deliver much bandwidth. Email and SMS, yes. Voice, only on slow days. Today's web, no way. It would be like building a network for Blackberries.
One of the more successful off-grid comm systems is SailMail.[1] This is worldwide email, over 10MHz, for boats. Down at 10MHz, radio can cross oceans. This was a side project of Stan Honey, who invented car navigation systems. He's seriously into sailing and holds records for crossing the Atlantic, sailing around the world, and such. So he developed this for the long-distance sail community. They maintain about 25 fixed stations around the world, and if you can connect to any of them over HF, you can send and receive email.
(STRIP was actually in the linux kernel, though I assume long gone or defunct -- the only things I still have talking via Ricochet are 2.4-era)
I have a couple of the lightpole radios (they listen for the modems on 900MHz and speak amongst themselves on 2.4GHz) and scored a single tower radio (talks to the lightpole radios and has an ethernet downlink) and have gotten them to speak with each other, but haven't had time to figure out the route mapping steps -- IIRC the deal is that the packet routing path information is stored upstream and delivered to the downstream radios. No idea if anyone ever decoded that format.
I messed around with this a lot in the immediate post-Ricochet era in between flashing silver WaveLAN cards to gold... fun times. It seems like it would be entirely possible now to run a simulated node using SDR.
Then why did we have 900 MHz analog cordless phones in the 1990s?
A mesh network is a completely different beast, with perhaps hundreds of thousands of nodes, spread around, and a good chuck of bandwidth being used for forwarding data between nodes.
Those 900MHz analog phones were also usually low power, low distance, analog only devices with a few number of channels. Try having dozens of those phones all in the same room and see how useful they all are at once.