updated 06:30 pm EDT, Tue July 9, 2013
Half-hour outage was the first serious problem since April
The iMessage system used by millions of Apple owners to send free SMS-like messages and multimedia files was temporarily offline earlier today for about a third of users, from approximately 12:35PM to 1:11PM Pacific Time (3:35-4:11PM Eastern). The outage meant that text and files would "fall back" to being sent by traditional SMS or MMS using the carrier of the mobile device if sent to an account with a phone number associated with it, but might fail if sent to an email address only. Apple offers the free iMessage service as part of both iOS 6 and OS X Mountain Lion.
The last time the iMessage system was down for a significant number of users was back in April, where two outages occurred in the space of a week's time. The initial outage in mid-April lasted for over five hours, an unusually long event. Mac users rely on the Messages app to handle both SMS and non-SMS messaging, chatting on multiple services, audio calling to other devices (apart from "landline" or non-Apple telephones) and file and screen sharing duties.
A separate but integrated program, FaceTime, handles video calling for both Macs and iOS devices. The service works with other recent Apple devices, but at present there is no version of Messages or FaceTime for other platforms. Windows users generally rely on Microsoft-owned Skype or a combination of other programs to fulfill most of these functions.
Apple also reports that iCloud mail was unavailable for 0.1 percent of users for a three-hour stretch on Sunday, July 7. All services are currently listed as operating normally.