Azure consumption services were made available through the Open programs from 1 August 2014 where you buy a $100 (or equivalent) token upfront to consume services against.

This Azure in Open FAQ contains some interesting facts:

• you must activate tokens within 5 years of purchase;
• you forfeit all your Azure in Open balance if you associate your subscription with an EA;
• and if you get to a zero balance then data is retained for 90 days.

Find the full FAQ here: http://bit.ly/1HdqBwY.