Thankfully I’ve yet to run into this - however if you’re using Android on AT&T you may find a need to use this workaround to load applications which AT&T blocks from your phone.

One example of such a blocked app is apparently PDANET which enables free tethering between your laptop and your Android phone — for no additional monthly fee.

It seems the trick to this whole workaround is to first take the SIM card out of your phone. Power your phone back on. Then download from the Android market to your heart’s content. This will work at least until the carrier(s) figure a way to shut it down.

(Source: Lifehacker)