According to the WP8.1 Beta SDK leaks, It seems there is no Mobile Data on/off option in quick settings. It's really unbelievable how would Microsoft forget to add that option! It's a really huge missing for the system and the coming update. Many people need that option. It's really interesting that Microsoft limits celluar download, brings DataSense to protect their wallet but doesn't let them to control their mobile data themselves!. Please fix this situation in the final build!
Mobile Data On/Off Option to Quick Settings! – Feature Suggestions for Windows Phone
Mobile Data On/Off Option to Quick Settings! – Feature Suggestions for Windows Phone