What is the area code for Miami?

305 for the Miami-Dade area and The Florida Keys, with overlay area code 786.

The country code for the United States (plus Canada and certain islands in or near the Caribbean) is +1.

(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.)