hi,
Wireless-controlled robots use rf circuits, which have the drawbacks of limited working range, limited frequency range and the limited control.
Use of a mobile phone for robotic control can overcome these limitations.
It provides the advantage of robust control, working range as large as the coverage area of the service provider.
How can i connect mobile to arduino board??
As dxw00d, the available RF modules that are compatiable with Arduinos can have significantly greater performance then standard RC controllers in any one limitation you mention and many times more than one. Furthermore, when you build an RF system you get to decide what to prioritize, so if you want a fairly long range even through most solid objects you can choose lower frequencies than commercial RF controllers use. The only reason we are trying to steer you away from using two cell phones with active subscriptions is that there are better (in basically any sense of the word "better") solutions already made and documented, try looking at the
Communications section of the Playground for examples and guides.
If you are dead set on using a moble phone to control your robot I'd use a GSM module, as described
here, on your robot instead of a second phone. You'd still need an extra SIM card with an active subscription. However, it's better than the way you want to do it because you can send signals directly to the electronics controlling your robot, instead of having to go the round about way of listening for key tones. You can also have two-way communication through text messages.