So after the release of iPhone OS 3.0 I found this guide about enabling tethering in countries where it is disabled by the carrier’s default configuration, and it has worked really well (I have an unlimited data plan, by the way).

With the release of iPhone OS 3.1 yesterday, rumors and early adopters say the firmware update would disable Internet Tethering on iPhones where the carrier doesn’t officially supports it.

I updated to iPhone OS 3.1 with certain precautions, and Internet Tethering is still functional for me.

So if you want to update to 3.1 without loosing the tethering capacity, this is what you should do:

DISCLAIMER FIRST: This worked for me, but I don’t have any way to know if it will work for you. Proceed at your own risk. If you already have enabled Internet Tethering and it is critical for you, I would recommend you to not follow any unsupported method like this.

Before updating to iTunes 9 make sure you have the last version of your carrier’s provisioning bundle:

1. On your iPhone go to Settings / General / About, and look for Carrier version. Take note of the version number. Mine was Telcel 4.4.
2. Download the list of iPhone OS updates from here, and find your carrier’s latest provisioning bundle available.
   My Carrier is Telcel México, so I found their last provisioning bundle is this:
   Telcel_mx 3.0 BuildVersion 4.4 BundleURL http://appldnld.apple.com.edgesuite.net/content.info.apple.com/iPhone/CarrierBundles/061-6937.20090803.3er5t/Telcel_mx.ipcc

   So, I’m up to date.

If you have the latest version of your carrier’s provisioning bundle you’re free to go; if not, you should first update it while you have iTunes 8.2, and possibly re-enable tethering using the aforementioned guide.

To install the iPhone OS 3.1 update:

1. Download and install iTunes 9.
2. Connect your iPhone, so iTunes 9 can search for updates. When iTunes says there’s an update for your iPhone DON’T UPDATE, choose to ONLY download the new firmware, but don’t install it just yet.
3. Sync your iPhone, so it is ready for upgrading (the backup can take several minutes sometimes). Then disconnect it from your computer.
4. Wait for iTunes to finish downloading your firmware update.
5. When the download finishes, enable Airplane Mode on your iPhone (first option of Settings). This will disconnect your iPhone from your cellphone network and WiFi.
6. Reconnect your iPhone and update your firmware (the one iTunes just downloaded). The operating system will be upgraded and your iPhone will restart. Don’t disconnect your iPhone until it shows up in iTunes, and you are sure it has upgraded to 3.1.
7. Disconnect your iPhone from your computer, disable Airplane mode and wait for your iPhone to reconnect to network.
8. Go and check in Settings if you still have Internet Tethering available as an option.

I have done this in two iPhones: First in my wife’s (she doesn’t use tethering, so I taught it was a good idea to test first on her iPhone) and later in mine.

Both iPhones showed the same carrier version after the firmware upgrade, but after a restart mine shows a different one (5.0). Anyway, tethering is still functional.

I suppose Internet Tethering option may disappear one of these days (when Telcel sends a new carrier configuration file to Apple), or they will start charging extra money, but in the mean time it is working well.

Good luck if you decide to upgrade.

DISCLAIMER: This information is provided AS IS, use it under your own risk. I’m not responsible if you broke your iPhone, or if your carrier charges you a lot of money, or if someone sues you.