Using WiFi won't eat up data, but if you lose the signal it could automatically switch to ... EV-DO ... and start using data without your realising it. 1GB would be enough by itself, the extra GB will be useful insurance for when you accidentally go on cellular data when you think you're on WiFi.
The word 'Pentaband' means '5 Bands', from the Greek word 'pente' meaning '5'. For a phone to be pentaband it has to support 5 bands. If the phone has AWS support, it doesn't automatically mean that it is pentaband.
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