I want to built a robot and i need bunch of modules to track it like GSM/GPS Wifi and Camera If i try to buy each of module separately it will cost me 300 dollar each aprox in Pakistan. On the other hand an android enable phone can be purchased on just 250$ having all of them. I was wondring if it is possible to interface android phones like (Huawaii or google nexus) with 8-bit microcontrollers or Arduino? The only port available with android phones are USB and Arduino supports USB. It is possible to some how attach both of them?
Yes, it is possible. You need the Android Accessory API and Android Accessory Development Kit. It is based off Arduino, and is open.
In general, if the phone + the ADK is cheaper than buying the components separately (I suspect it would be), then I'd buy the phone + ADK.
Your other option is to buy a phone, and a bluetooth shield for a microcontroller, then use the bluetooth connection to send data between the phone and microcontroller.