Yesterday, I removed my SIM　card from my Galaxy S. And then I turned it on. So that, I can use it as a wifi device only. After I did some tasks, I plugged back the SIM card into the phone. Then I had a problem. The user data are gone! I did debug on my phone. I found SQLite database are gone!!!!! As a result, I have to uninstall apps and install them again! This is the only way to make those apps work again! So poor. So, please re-think before you remove your sim card from Galaxy S. That may be a problem which is unique in my phone, but you should be still cautious about that!