拨打 is more formal than 打 (dǎ) for making phone calls. You'll hear 拨打 in automated phone prompts and official announcements. In everyday speech, just say 打电话 (dǎ diànhuà).
culture
Key Chinese emergency numbers: 110 (police), 119 (fire), 120 (ambulance). These are read digit by digit: yāo yāo líng, yāo yāo jiǔ, yāo èr líng (1 is pronounced yāo to avoid confusion with 7).
