Both AnkiDroid and the iOS Anki support syncing, so then all reviews can place on the device without using any data and then synced later in the day.

I do this myself and it works well: most of my Anki reviews each day take place using my phone when travelling without any signal on the metro.

True but I resent having to pay £17.49 to cover the development costs for the other platforms. (I think the android version was developed by someone else which is why its free)

Did you try their mobile apps? I suppose after syncing, the decks would be stored locally on the mobile.

I used the android app before but since I broke that phone, I'm using an iPhone and just can't bring myself to pay that much.