1. Your phone contract provides international roaming services.
Keep in mind, roaming can be very expensive. If you just want to have your phone for emergencies, then this is probably OK. But if you’re planning on using your phone a lot (which can be very convenient from making reservations to allowing the tailor to get in touch with you as soon as your new garments are ready for their first fitting), I’d think about looking at #2.
2. You have an unlocked phone.
With an unlocked phone you can simply buy a pre-paid SIM card (often available from shops within the airport, metro stations or nearby hotels at stalls and convenience stores). The cost for a SIM card is anywhere between 100-200rmb and will have minutes already included. You can top-up your minutes buy buying phone cards (available from convenience stores and stalls) in amounts up to 100rmb. Rates are very reasonable and the menu for recharging your phone is available in English and Mandarin.
Mobile phone vocabulary list
You can use this vocabulary listing to help you purchase a new SIM card, re-charge cards and other accessories during your stay.