I installed CyanogenMod on my HTC Desire about a week ago in an attempt to get rid of some of the crapware that Orange UK are notorious for installing, and get a snappier, cleaner phone. I won’t repeat the excellent CyanogenMod install instructions, which you can find here. However, here are some points that might help you if you’re doing something similar:
The OS (Android) firmware and the radio firmware are two separate things. The phone was at the latest Orange-approved firmware level before the upgrade (Android 2.2, which comes with the radio at version 5.10.05.30). I had read elsewhere that Orange network-lock the phone and that this sometimes causes problems when installing CyanogenMod; so I deliberately removed the SIM card during the upgrade process as suggested. Whether this circumvented the problem or whether it simply wasn’t an issue I can’t say, but certainly I haven’t seen any network-lock problems. I didn’t upgrade the radio at all, as this seemed risky; I simply left it at the 5.10 level and skipped over that section in the install instructions.
After the upgrade, I was initially nervous that the 3G had stopped working, as sitting in my house I simply couldn’t cause the phone to roam onto 3G or HSDPA; however, it seems that it simply has different criteria for roaming onto 3G - it will keep a stable slower signal in preference to a poor faster one. In fact, so far I seem to get a more reliable data signal, and the phone uses 3G and HSDPA just fine when it can find a good signal.
Update 22:30 I found I needed to apply this workaround in order to be able to install large applications such as Google Maps.
As a result of upgrading it, the phone is a lot faster and smoother. Much of the jerkiness has disappeared from the user interface - even third-party apps such as Twitter work more smoothly. The most astonishing thing is the battery life, which seems to have almost trebled - whereas previous the phone would struggle to last a day, it now lasts over two. This is quite impressive - I’m not sure what was dragging down the phone before (HTC Sense, perhaps), but kudos to the guys at CyanogenMod.
In summary, CyanogenMod seems like a way of getting a clean, modern, Android build onto your phone. Some of the menus do stuff from a plethora of options, but the defaults are fine, so it’s a great way of getting a “plain” Android phone. Recommended.