I can see two major drawbacks with that - the connection speed will range from abysmal to quite low and the screen size will make it virtually impossible to see what you are doing.

I would have thought a laptop is an absolute essential along with either the 3 or Vodaphone USB Broadband stick. That way you keep a copy of the website on the laptop, make the changes that you need and upload them. Even then, upload speed will be very low indeed and you are in danger of losing the connection part way through.