SureCop uses SMS as communication medium. That’s why it works on phones with no internet connectivity. The person who finds your phone can replace the SIM card that does not have a data plan. In such situations the online phone tracking solutions will not work as they cannot reach the phone.
Besides some online phone trackers requires use of desktop PC to issue remote commands to lost or stolen phones. This might not be possible all the time as you might be on the road or watching a movie in the theatre etc.