It has always been a tactic of large communication companies to make their invoices confusing for the customer to read - Remember the famous line from Theresa Gattung where she said its used confusion (telecom) as it's chief marketing tool. However I have in front of me one of the best laid out invoices I have seen from a teleco. As I have a background in building software based billing engines I usually take notice more than most of how companies invoices are structured and displayed to the customer.
Here are a few things that they do really well
Most Frequently Called - top 10
Most Expensive - top 10
Most freq texted - top 10
Service summary
Nice clear layout which is really easy to read, it makes it easy for you to workout which plan would best work for you - best mates etc.