Recommended SIP to Cellular Gateways?

One of our customers wants to have a fallback option for voice alarm notification at a remote site. Does anyone have a good recommendations for a SIP Cellular Gateway? I’ve used the Grandstream SIP to POTS gateways before and had good luck, but I can’t seem to find a similar product from them that goes directly to cellular. I’d rather not have two devices - a cell modem like a cradlepoint in front of a grandstream - if at all possible.

Use one of the Twilio modules?

I was a bit unclear: they want a fallback option in case the internet connection fails. As far as I can tell the Twilio modules require internet access in order to function, correct?