So to start with, there is only one accurate way to track your data usage.
That is through your Network.
No third party app can do this due to the technology that the networks use.
There are myriad Apps available in the Market which claim to accurately track your data usage, this is only somewhat true.
So you ask why can they not track my usage accurately?
The applications can only track the data that actually arrives at you phone, they have no way of tracking “Packet Loss”
So you ask what is Packet Loss?
As the network sends you packets of data some get lost. To ensure you get you the correct data to your phone the network then resends the lost packets. This increases the amount of data you consume. So for a very basic example, you try to download a 1Mb file. Due to packet loss, only 900Kb gets to your phone. The network sees that you only received 900Kb so sends the missing 124Kb again. This means you have consumed roughly 1.1Mb to get your 1Mb file. The apps on your phone will show 1Mb received which is accurate. Your phone has only received 1Mb but the Apps have no way of knowing what the network conditions were at the time and how many packets were lost.
So where dose that leave you? If you use one of these Apps it will give you a rough estimate of your data use. It should never be treated as anything other than a rough estimate.
If you want to know exactly how much data you have used, check through your network.
All the networks now let you login to your account online and you can check your usage there but bare in mind they can be behind time as their system has to update everyone’s usage.
Some Networks now offer their own account apps and these will be preferable where available.
So what third party App should you use if a network one isn’t available?
On every Android phone I’ve had I have defaulted to downloading and using an App called “3G Watchdog” (download here)
I have found this to be the most reliable and least draining on the battery. It also has several settings so you can adjust it to suit your needs.
From experience it is usually shows about 10% less data usage than what the Network is reporting but this will vary depending on what your network conditions are like so don’t use that as a guide, compare it to what results you are getting.
Some reviews on the Market have said it is heavy on battery drain. I have never found this. You can set the frequency it updates within the App. Obviously if you have it updating every minute it will consume power but why would you need it to update the often?
Let us know what your experiences are in the comments below. What Apps do you use?