What is baseband?

I'm not sure what it is exactly but I know that the lower your baseband the more likely you are to be able to unlock your phone so you can use it on any carrier. I don't really know much about them cause I always get my iPhones unlocked so I don't have to worry about preserving a certain baseband.

Edit: after some quick googling I found this "iPhone baseband is essentially the cellular modem firmware that is on your iPhone. You’ll probably have heard of baseband upgrades, the purpose of these upgrades is to improve the functionality of the cellular modem and also to keep the device locked to the intended carrier (in the USA, this is AT&T).

This is why iPhone unlocks are updated and specific to different baseband versions, since ‘hacking’ the baseband is necessary to allow the jailbreak and unlocked iPhone to utilize the cellular modem on the phone, thereby allowing call, data, and SMS transfer to occur on the device." http://osxdaily.com/2010/08/09/what-is-iphone-baseband/

 

Baseband = the firmware that the radio part of your phone uses.

 

The baseband is what the previous poster said, the radio your iPhone uses. Basically it's better to have a lower baseband because the lower the number, the earlier they came out (usually), which means that an unlock is more likely to have been developed for the lower basebands. However, not much progress has been made on an unlock that depends on the baseband in a long time, and with the availability of unlocked iPhone models in the USA directly at Apple stores, the focus on baseband unlocking has become a bit less of a big deal.