I’ve been playing with the Digi Xbee 3 cellular devices. Digi has their Remote Manager platform that provides many of the device management features. I used it for a while with some of their larger devices such as their industrial cellular gateways. The pricing / billing was not as friendly as Particle but that was several years ago. I can’t speak to their current model.
One caution about using the Xbee 3 with a Hologram SIM…Digi puts their own AT command set on top of the cellular module by default. I found that configuring the device and troubleshooting connections was a little limited. You can bypass the Digi abstraction but then the development experience is a little less refined. Hologram has suggested it is worth the effort to have more control of cellular module configuration.