How much data is this actually likely to use? Effectively plain text data doesn't seem like it should be expensive. Even with something like .odt you're looking at a few KB a 'page.'
There are other concerns than just the amount of KB transfered.
When connectivity is poor SMS is much more likely to work than data (2G/3G/4G).
AFAIK. GCM is not a "true" push service, it just provide an API that makes it seem like one.
Battery use is much higher for data, especially when you are in a location with bad connectivity.
Some people prefer disabling data when they don't need it, for the reasons above and for other reasons.
Most people disable their mobile data when roaming, because fees are set to bleed the unfortunate few who forget to dry. If you live in a country that is only a few hours drive to neighboring ones, that's something you do quite often. So SMS is not only more likely to work, it is absolutely required.
Yeah, but you need to then configure your phone to make sure only TextSecure uses roaming. If anyone knows an effective way of doing this (that is not manually disabling everything else) I would love to hear it.