Well, it depends.Originally Posted by toddniem
The Kindle can update the books location whenever it has an Internet connection.
So if you have either Kindle 1,2 or Kindle DX white, it definitely has a 3G connection and can update anytime.
If you have a Kindle 3, or Kindle DX graphite, it depends on whether you bought the 3G version. If the kindle is wifi only, you obviously need to update before leaving home.
Edit: Only Kindle 3, or Kindle DX 2 have wifi and you mentioned it connects via Wifi at home, so it really depends on what device you bought.