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Somebody correct me if I'm wrong but the reason why Siri needs the internet is because translating and interpreting your voice is done off the device. Your instruction/command is sent via the internet to Apple's servers where it is interpreted and converted into something that Siri can understand. It is then back to Siri on your device.
 
This is why we would need a 32GB iPhone to be the minimum before moving to offline-Siri. No doubt it would take up a chunk of the storage.
 
This is why we would need a 32GB iPhone to be the minimum before moving to offline-Siri. No doubt it would take up a chunk of the storage.

You can use offline voice control on an 8gb android phone.

Also, if you disable Siri, it reverts to voice control which works without internet but is limited to playing music. But it is at leastsmart enough to understand you say album, song, music, or specific random band/album names
 
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