What is the area code for Baltimore Maryland?

Area code 410, with overlay codes 443 and 667.

The country code for the United States (plus Canada and certain Caribbean islands) is +1, which is dialed as 00 1 from most of Europe, 010 1 from Japan, 0011 1 from Australia, and so on. Dial your international access prefix, then country code 1, the three-digit area code, and the 7-digit subscriber number.

(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.)