Patricia,
You may know that you are looking at AC at an interesting time since the practice management portion of the program does not yet exist, and the company is in the process of deciding how to move ahead with some sort of integrated billing solution. There are some elements of billing software in the current version; there will be additional ones in V6.5 which will be available soon. Nonetheless, if you use AC, you should realize that it is primarily an excellent EMR. All current users have had to develop a system for billing beyond AC and there are many different ways to do so. None are ideal as none are fully integrated with AC.
Sometimes it is hard to imagine new workflows. I would bet that you will find that there are many things that AC does far better than your current Allscripts product; the juncture between performing the note and sending the bill may be an area that is more difficult. Or maybe not. Can you describe your billing situation a bit more so that AC users in similar circumstances might be able to offer more information? Will you outsource your billing or do it on site? How do you handle it now? Are you aware that with AC you can print a daily batch of invoices or 1500's, or do them individually?