Also, I had a look at the IM application and I modified it to allow login instead of having the "phone number cannot be read from your SIM" error. This might or might not work. It works for me, but users in the US have reported that it still fails.
UPDATE 16th Jun 2010:
Added version 1.1.2 from Cliq.
UPDATE 3rd Feb 2010:
New eclair version for IM.apk, completely untested. Might or might not work.
Patched ImProvider is no longer useful for Android versions >= 2.
Also, I removed the cupcake IM.apk because I just noticed it is broken and won't work. No-one should be still running a rooted cupcake anyway.
This is for donut. I tested it on cm 4.2.2 and 184.108.40.206, but it should work with any donut rom. As far as I know, it doesn't use sms at all. It still needs the tmo plugins to login, but no sms are sent. Other than that, it does exactly the same as when you login on wifi.
Some of these steps will fail depending on the rom (the dalvik-cache and odex part). These errors can be safely ignored.
First reboot into recovery, then, on your computer :
adb shell mount /system mount /sdcard cp /system/app/IM.apk /sdcard/IM.apk cp /system/app/ImProvider.apk /sdcard/ImProvider.apk exit adb push ImProvider.zip /system/app/ImProvider.apk adb push IM.zip /system/app/IM.apk adb shell mount /system/sd rm /system/sd/dalvik-cache/* rm /system/app/ImProvider.odex rm /system/app/IM.odex umount /system/sd umount /system umount /sdcard reboot
More information about the sources is available in this post.