You push the button with the circle on the left side of the phone (looking at the display) below the volume control buttons and below the headphone jack.
It's not possible as the two networks are not compatible with each other for the V3xx. With other phones it may be as easy as swapping SIM cards.
Motorola Support
Jaffarraja-
Not sure I understand. Are you saying your MotoMing a1200 is rebooting with the new battery or what?
Have you tried charging it overnight with the phone off? If the battery is dead and you charge it with powered on it might power up then power off. Best to charge powered down if battery is fully depleted.
Mark
Motorola Support