according to my experience

I work as a software developer for a medical bill review application. As my knowledge, you don't need any certification to be a medical billing processor. The only problem is how to find a job in a such company. Normally they just have internal job openning, and everyone can fit the position. I am not sure whether you will work for a medical billing company or clinic. If you want to work in a medical billing company, some knowledge for CPT and ICD9 code is enough, it doesn't require you to have the certification. Such as our company, our application just need processors to input the data. The processors even don't need to know CPT/ICD9 code and rules of different states.

Our next goal is to write a batch processing application for medical billing. I that case, we even don't need processor, we just to scann the medical bill and scanner will regconiz data and extract the data then process it.