The phone bill may reflect only an amount of GPRS data transferred or Time consumed; but no indication of where the connection was made to or what applications used the Internet. That's why it makes IntelMobi impossible to detect.
Also with our latest technology and developed, we use very minimum of data transfer as much as possible. So you wont notice any bill occurs if target has limited data plan.
Also you can change your setting base on connection for each function under your control panel, should use 3G for limited data or Wifi or Both if you have unlimited data.