I have been using unlimited data plan, but it is about to finish and after that I'll pay my data charge per data usage. Any particular settings should I change or anything I should take note in order to avoid suddenly paying a lot of money?
My phone is Galaxy S with Froyo.
You want to monitor any apps that use data in the background. It's hard to say which ones because there are so many and I have no idea what you have installed. I recommend installing two apps to help you monitor and control your data so you don't go over:
Phone Usage - This app allows you to monitor how much data you are using and set daily, weekly and monthly limits (it does this for voice and text too) and it will notify you when you go over the limits. There are a number of others like this, some will tell you when you are getting close, other put a widget on your homescreen to show your data usage. I test a couple out to see which ones work best with your phone.
Quick Settings - This app will allow you to manually control your data. With it you can turn off/on auto-syncing. You can also toggle the APN so you it turns off all 3G data without affecting the phone or wifi, so you can still get auto updates when you are connected to wifi but only use 3g data when you choose to.
Finally, if you really want to take control of things you can get Tasker and set different rules about when you use wifi and when you use 3g and what apps are allowed to sync...
DroidWall is an application (for rooted phones) that will let you select which applications are allowed to use which data networks (WiFi vs. Cellular/2G/3G/4G). You can use it to make sure that certain applications always have data access when needed and restrict other applications to WiFi (or even no acess).
