The guide comes by way of Hexxeh and it’s pretty straightforward. As with any of these kinds of modifications, though, you’ll want to proceed at your own risk and know that it could “break” at any time. This is experimental, after all.
1. Pop your SIM card into the slot under the battery (must be a full-size SIM, microSIMs you’ll just lose in there, fine if you use an adaptor though)
2. Make sure you’ve enabled developer mode – do this by flipping the switch under your battery
3. Once you’re booted into developer mode and logged in, press Control-Alt-T
4. This opens crosh, a limited command shell. Since we’re in developer mode, we can get a full shell. Type the word shell and press enter.
5. You’ll get a shell that starts with ‘[email protected] / $’. Once you’ve got this, we can type in the command that flips over to GSM.
6. Type the following command: modem_set_carrier “Generic UMTS”
7. Wait a couple of minutes, then you can exit the shell by typing exit twice.
8. Your 3G should be usable assuming you have an active service plan on that SIM card, and that ChromeOS knows your APN settings.
It won’t be able to show you usage details, so be careful with whatever data plan you intend on using. You’ll also need to make sure that your APN details are already hardcoded as part of the list in flimflam.
Based on early tests, the GSM is working and people are able to get up to 4Mbps down through AT&T.