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It can be hard to find the setting for this, but one way you can keep Gmail from automatically synching is to go into your device's SETTINGS menu, then ACCOUNTS & SYNC. You can un-check auto-synch, but that will disable it for all applications. Under ACCOUNTS & SYNC choose MANAGE ACCOUNTS and pick your Google account (probably the only one on the phone unless you have multiple accounts for personal/work). There is a list of applications to sync (Drive, Google Play Music, Google Photos,......Gmail). If you uncheck the box beside Gmail it will not synch automatically, and it should stop it from hogging your bandwidth. You will need to open the Gmail app and manually choose to refresh to check your mail though. Maybe there is another way to do it, but this is the only one I can think of off the top of my head. I am not familiar with Kyocera phones (although my office once had an awesome Kyocera copier), but the basic steps should be the same across devices.