Most modern handsets offer Android 2.3 nowadays, but what about older phones? Most legacy devices are stuck to Android 1.6 or even 1.5, because their manufacturers abandoned them, concentrating on new models. HTC has promised its customers, that HTC Tattoo (also known as HTC Click) was going to get update from 1.6 to 2.1 at some point. Unfortunately, Eclair was newer released for this terminal. The last stock ROM for this device is 1.67.405.70, which is based on Android 1.6 and HTC Sense for QVGA.
Fear not, you still have a chance to install more recent Android version on your phone. Some third party developers (namely a guy known as cn.fyodor) took matters into their own hands, and released a custom ROM, which runs Froyo on HTC Tattoo. Most known issues have now been removed and the last stable version is available for download from this link (xda-developers).
Another nice build for HTC Tattoo is the newest nFinityGB 1.03 running on Android Gingerbread 2.3.4. This build is available on xda-developers.com.
To make sure GPS is working, leave it on in the old ROM, otherwise it might not work after flashing 2.3.
WARNING: To install custom ROMs you need to root your Tattoo first and then install ClockworkMod.