I was actually more interested in knowing what kind of security is inherent in tethering. Any advice?
Honestly, GSM hacking isn't nearly as difficult as it was just a year or two ago. To answer your question as far as what kind of security tethering offers the simple answer is none. It is more security through obscurity. The caveat here is that in order to be able to sniff GSM packets you will need over $1000 worth of hardware. Then again this same hardware 1-2 years ago cost closer to $10,000.
To sniff wifi traffic you just need a laptop (even most netbooks will do fine), some freely available software, and a wireless card that allows it to enter monitor mode.
As far as WPA2 is by no means uncrackable, but it is significantly more time consuming than something like WEP. On a WEP encrypted network that sees some decent traffic it will often take as little as 5 minutes to crack.
WPA2 is much more secure (the hash for the handshake is salted by the SSID you are connecting to) but is still susceptible to attack primarily via intercepting the parts of the four way handshake (transmitted when devices join the target network) and comparing the hashes to Rainbow Tables. Basically, it is akin to taking a dictionary of common passwords and their associated handshake/SSID's and comparing them to what you see in the packet capture. However, if you use a non-standard SSID you are much more safe while using WPA2 because odds are high that the attacker doesn't have rainbow tables for your corresponding SSID.
In the end, if you are that paranoid and the network you are connecting to is either unencrypted or encrypted with WEP you will be much safer tethering your phone. That said, there is one further caveat. When you tether you should tether either via USB cable or via Bluetooth. If you tether via wifi to your phone then you have the exact same vulnerability as if you were connecting to the local wifi network.
Basically, while GSM networks ARE vulnerable to sniffing it requires a much larger investment in hardware to be able to. Wifi sniffing is dirt cheep and simple to do.
Hope this helps clarify a bit further.