Heidi and I have iPhones, which in the US means we have AT&T as a wireless provider. We signed up for automatic payment on the second month and it's been working pretty smoothly.
Except last month. AT&T was three days late taking the money out of my account (which had a healthy balance - they delay must have bene on their end) and now they sent me a bill that specifies that I am (1) overdue on last month's payment and MUST pay this right away and (2) I should not pay anything because they will take the money out of my account automatically.
Whatever geniuses designed their billing system and form letter generation system need to have their heads examined. It'd be amusing if it weren't such a sad display of incompetence.