Where is telephone country code 1931?

Country code +1 (dialed as 00 1 from many places) is North America (US, Canada, etc.); the 93 is the first two digits of a three-digit area code. You need the next digit to know where, but it happens that as of 2012 all +1 93X numbers are in the US or Puerto Rico.

• +1 931: Clarksville, TN, USA
• +1 936: Huntsville/Nacogdoches, TX, USA
• +1 937: Dayton, OH, USA
• +1 938: Huntsville, AL, USA (overlay of +1 256)
• +1 939: Puerto Rico (overlay of +1 787)

(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.)