I am developing an Android app that needs to communicate bi-directionally with a server. By that, I mean either the server or the device can send a message at any time, with an arbitrary amount of time in between messages. Sending data from the device to the server is a common and I think well understood task, but I'm not as sure what the best approach is to go in the opposite direction from the server to the device.

I think having the device periodically poll the server may be a bad idea due to latency and the drain on the battery, but I'd be willing to consider this option. My plan at the moment is to send text messages from the server via an email-to-SMS bridge, and to have my app run a service to receive and handle these messages.

The question I have is if there are any best practices for this scenario, and if using text messages has some downsides that I have failed to consider. For the sake of this question, I want to assume that users have an unlimited text data plan, so paying per text won't be an issue.