LeanStack interviews startup founders about the technology stacks and infrastructure behind their products.
HN commenters link its interviews with Algolia, Authy and StatusPage.io as sources on how those services were built.
Authy (a two-factor auth service) uses a combination of Twilio and BulkSMS (they say that BulkSMS is particularly good for Latin America). Authy explains how they handle global SMS here: http://blog.leanstack.io/how-authy-built-a-fault-tolerant-two-factor-authentication-service/#bulksms
Here's an interview with the founders of StatusPage.io and about how they built it. You might find it interesting. In the end they stuck with what they knew - Rails.
http://blog.leanstack.io/how-statuspage-io-was-built/
We have done an interview with Leanstack.io where we discuss our infrastructure: http://blog.leanstack.io/how-algolia-built-their-realtime-search-as-a-service-product