The Import Export Code is a 10 digit special code provided by the Director General of Foreign Trade, Ministry of Commerce, Government of India.
Technically speaking, an IEC is necessary for any person looking at making an import into India or exporting a product or service out of India. So technically speaking, if I create even one software program and sell it to a party based in the United States, it is an export and I need to get an IEC.
Practically speaking however, you only need an IEC if you are going to be making sizeable exports and your income from export of services is more than Rs. 9 lakhs. In this case, getting an IEC will make you eligible to get a service tax exemption.