One of our phones is on a plan with a data limit. It's never been an issue before, but now we're suddenly approaching our data limits. Does data accessed while connected via WiFi count towards the data limit? I would assume not, so possibly hubby is streaming Sirius and not realizing that he isn't connected.
WiFi data does not count towards your data limit.
However, sometimes you can think you are on WiFi when you are not actually on it.
You could try using an app called Onavo Count which can restrict other apps to only WiFi data.
No, using wi-fi doesn't count against your data charge. But, the wi-fi might be going to sleep if the screen is off. If so, then cellular data will be active again if it's still turned on. To be on the safe side, you may want to turn cellular data off when using wi-fi.
After looking at the iPhone version of the app, it may not be able to restrict an app to wifi data like the android app does. I am not sure, as I have not used the iPhone version of this app and will have to check for yourself. You would be able to keep track of which apps are using the most data, though.
Keep in mind, it has been reported several places on this forum that when an iPhone is in sleep mode(screen off) wifi is somehow turned off and the phone reverts back to cellular data. To prevent this from happening, it may be safest to turn off cellular data if you are streaming something and think you are using only wifi as a data source.