My app says I’ve used 28% of 24GB, with 13 days remaining this monthly cycle.
That means I use roughly 12 GB per month. My wife and I share the data in a “datapool” (12GB each, so a combined 24 GB), but I use most of it. 🙂 Apple Music counts towards data usage, but Spotify music streaming would not (if I went that route). I chose Apple Music because I may buy an Apple Watch with LTE soon!!
I’m in Australia, FWIW