Why do you feel you need two devices?

3G certainly won't be a viable alternative, its too variable and unpredictable, and also coupled to the fact that many Mobile companies are actually taking a step backwards, and removing previously offered options such as Tethering.

Then there is the hidden capping, throttling, fair use policies etc which comes with those so called 'unlimited' deals.

Despite the rise in Mobile Internet use, the industry is about as restrictive in terms of what the customer can and can't do, and what they can and can't use as its ever been.

That's what a backup is

Yes, I understand what a backup is but most things that are "backups" don't have recurring fees and most people don't have a backup phone.