With the ViP622, I'm thinking it was since the L4.01 release....
Look at the Diagnostics screen:
 - Menu, 6, 3
 - Up twice to Counters
 - Select
 - Page Down once for Item 13), or twice for Item 21) below.
Although "13) Last Connect" has the normal monthly call-in, there is now a new item, "
21) Status scheduled: mm/dd/07 hh:mm am", which changes about every 9 days (?).  On 21), the time seems to stay the same, but the date will update.
And if you page down to the 4th screen, you'll see "07) Fsck: 1: mm-dd-07 h:mm am" which is the time it downloads each day to update the EPG (but doesn't call in).
Sorry, I don't know why the new call in time, but maybe:
 - Performance reporting of your system, so that they can revise software.
 
 
 - Survey, i.e., what have you been watching. 
 
 
 - Checking to see who is not keeping the receivers connected to a phone line.
 
EDIT:
Actually, the more I think about it, it may have been just before the L4.01 release.
