You can request balance warnings and auto invoices to be sent to your email in your Financial → 'Preferences' tab. You cannot receive your monthly usage via email, but you can download all sent and received SMS from the preceding 90 days in a file; just go to SMS → SMS Overview → 'Export' tab.
Reporting for Subaccounts
Each Subaccount has the option to view their statistics in their Dashboard, as well as make an export for the messages sent. Since Subaccounts do not have their own billing log, all financial matters are managed by the main account holder.