If you go to AT&T and say "I want 10,000 SIMs that'll let me use a few kilobytes of data a day, with enterprise management features", they either won't sell them to you or will sell them at prices comparable to Twilio (except they won't work when out of range of an AT&T tower, and certainly won't work overseas). Their minimum pay-as-you-go plan that includes any data at all seems to be about $30/mo - if you're using maybe 10 kilobytes a day, that's not feasible.