Great question — answering as the UphillTech team:
It is not possible with no integration. Think about it... at some point your messages must be injected into the mobile network to be routed to the user's phone. That requires that you have a connection or a gateway on that mobile network. The messages cannot get onto the network without some kind of integration. There are three main options Use the providers' SMS gateways. Many providers have publicly available SMS gateways that will route messages to/from their customers. You send your message to their gateways and they store and route the message. Think of it as a mail server, which in many cases is in fact true as the gateway often processes SMTP traffic. You will need to track your...
Full answer by Doug: https://stackoverflow.stackexchange.com/a/59389385 (CC BY-SA 4.0).
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