You got that right. Yes, each one has a different billing cycle depending on when you signed up. However you would expect that if you signed up on 3rd of a month, you billing cycle would be 3rd to the 2nd of next month. This would be perfectly fine.
But have you noticed the there is a regulatory cost recovery charge on you bill. This amount I belive, is $1.25 for a month. But even if your billing cycle is 3 days, you still pay $1.25 and not "pro-rated". I think it is the same with Universal Svc charge. These are like fixed amount irrespective of the number of days in the billing cycle. No one would mind if instead of 30 days it was 25 days. But for 3 days to be charged the full amount of these mandatory charges is kind of unfair. And the government or FTC does not insist on cingular making the first 3 days as the billing cycle for the first bill. It is just cingular who has this wierd practice. Obviously they dont care since it does not increase their cost. However it does increase the cost to the constomer that he pays the fixed cost for only 3 days of service instead of 30 days.
Anyway, no point in pursuing this point here since only the cingular reps can answer why they send a bill out after 3 days instead of a month. I guess they just want to collect the money from you ASAP and dont care if you pay a few dollars more.