What is iPhone Baseband?
All iPhones have a baseband, and iPhone baseband is essentially the cellular modem firmware that is on your iPhone. Specifically, baseband includes the low level software that is running on the iPhones cellular modem hardware, the combination of which allows the iPhone to connect to a cellular network to send and receive data, phone calls, and transmissions.
Many iPhone owners have probably heard the the term “baseband” or perhaps read or heard about baseband upgrades. The purpose of these iPhone baseband upgrades is to improve the functionality of the cellular modem that is on the device, and the low level firmware (software) that is contained within the baseband.
Additionally, baseband is also what keeps the device locked to the intended carrier, in the USA, this is commonly AT&T, Verizon, T-Mobile, Sprint, and some smaller other carriers. Buying an unlocked iPhone would not have that baseband lock, for example.
This is why when certain hardware and software iPhone unlocks are updated they are specific to different baseband versions, since modifying or ‘hacking’ the baseband is necessary to allow either a software based unlock or jailbreak on the unlocked iPhone to utilize the cellular modem on the phone, thereby allowing call, data, and SMS transfer to occur on the device. Again, buying an unlocked iPhone does not require those modifications to baseband to access other networks, which is why unlocked iPhones are generally more desirable on the resale market and for international travelers than locked iPhones, which either must be unlocked through the carrier, or through a mechanism as described a moment ago.
If you ever need to find an iPhone baseband version number, these instructions show you how to do that.