How many bytes will be used with a mobile callback?

[hust]

Today, i make a mobile callback test in order to know how many bytes will be used ?

First, i have set a callback at my Voxalot account,with Voipdiscount's 2 legs. the first number is my mobile,the second number is a friend's.

After that ,i used my mobile to visit mobile.voxalot.com,and input ID\password,and make the callback. call duration is about 86seconds(the first leg,the 2th leg is 68seconds)

After one hour,i got the data traffic from my mobile carrier:
1 up direction: 4K bytes;
2 down direction: 4k bytes;
total: 8k bytes

NOTE: 1K bytes is the basic billing unit of my mobile carrier
I use a CDMA 1XRTT mobile phone.