Unless you use end-to-end encryption with sufficient cryptographic strength, the government can intercept your communication if it wants to.

Relating to your question, it means it doesn't matter whether you use GSM or WiFi. You need to encrypt your communication so that only the recipient knows how to decrypt it.

If you only want to hide your identity and do not care about your messages being intercepted, then something like using Tor network is recommended. But even that is not foolproof as shown by various research projects.

This is just my little understanding of the subject, the specific answer what measures you need to take depends on if you want to make your message unknown or your identity unknown - or both.

Just to make it clear, I don't think the "tablet mode" has anything to do with deterring the prying eyes of the government.