What is the international access code and country code for US?

The United States is part of the North American Numbering Plan (NANP), which is telephone country code +1.

The international access prefix for outbound international calls from North America is 011.

The international access prefix for inbound calls to North America depends on where the caller is located.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)