My Nokia 920 has the Portico update and it's been on constant Wi-Fi for the last 2 days. I just checked my data usage and it's still used 8 MB for those days. Anyone know why?
first: at&t won't charge usage if connected to wifi. UNLESS you are using your device as a hotspot.
second: because you are using wifi to transfer data, it's showing the 8meg.
I believe that all carriers charge the data contract price per month whether you use any carrier data at all. That's why the contract is priced as it is. As for incremental data use while on WiFi, it's probably something that needs data but can't get it from WiFi. that;s my best guess.
I don't think AT&T counts MMS against data since MMS falls under unlimited messaging. I know Verizon and T-Mobile handles MMS like that, so I assume AT&T does the same since it would be false advertisement otherwise.