How you bill is going to depend on the type of provider you are billing for and the scope of practice for that level provider in your state.
For instance: Psychistrists and physicians can bill either a 90801 (per episode of care) and therapy codes w/ medication management or from the 99xxx E/M codes. (Learn what constitues an episode of care. It's important.) An APNP can bill from the Behavioral Health codes and/or 99xxx codes by scope of practice. However, Psychologists, Behavioral Health Specialists may not use the 99xxx codes in most states. In Wisconsin, the state indicates that E/M codes include medication management. Since psychologists and others may not prescribe or provide medication management, they are not allowed to bill E/M codes 99xxx.
A good reference, though not updated for the new in 2007 testing codes, is: CPT Handbook for Psychiatrists, 3rd Edition by Chester W Schmidt Jr., M.D.; Rebecca K. Yowell, & Ellen Jaffe. American Psychiatric Publishing, Inc.
Also refer to your state's Medicare Carrier website for policy guidelines. Check with your state's Medicaid department to obtain a handbook on what can and can't be billed/covered by them.
Resources above will give you the minimum requirements needed for documentation to support the services billed, frequency, etc. You'll find most commercial carriers following Medicare guidelines. Also be aware that many insurance companies offer limited or no coverage for Behavioral Health issues for their policy holders.