u/Moxie479

We are a VOIP carrier and looking to implement POTS in a box type services. Our client is looking for boxes similar to granite EPIK and Ooma boxes that have multiple POTS lines and Will accept multiple SIM cards and then do SIP connections over the Internet and output as Analog POTS lines. We can rig something up using grandstream ATAs and LTE modems, but those POTS in a Box solutions are so clean. Is anyone aware of any hardware that we can use with our service that competes with those products?