All work must be completed via your smartphone in the store / at the job location.
While you do not need internet access to complete most Field Agent work, you do need to be connected to your telephone network service provider (3G). That should be all you need to enter and send in complete and accurate data.
There may be some jobs in which the instructions encourage you to connect to WiFi before sending in (submitting) your results. You still need to gather the results and enter the information into the app while in the store / at the job location, before leaving to upload your job from a WiFi area. All GPS data is secured while entering the data into the app, not in submission.