Using Google Voice in China is illegal, but it will be very convenient if you can obtain one before entering United States, as a temporary phone number to receiver phone calls and delivery information before your physical US SIM cards arrive. In fact, you can use your physical SIM phone line number to register a Google Voice number fou your personal Google account for free in United States, which you can take to anywhere you want after you leave from United States. But, remember that Google Voice number is a VoIP phone number, so it cannot be used to register ChatGPT, Discord, Paypal US, Twitter etc.