Hi Corrie,
InfoPath let's you create a custom section and that section can query a SharePoint list containing the customers. If your customers are in a different location, you can use a Web service. No custom code required, but you won't get type ahead. SharePoint 2010 will support sorting. You can connect to a REST Web service and specify sorting options when you do. Check out Qdabra's YouTube channel for REST techniques. No code required.
So, to summarize, if your customers are stored in SharePoint or behind some Web service, it's easy.
Best of luck,
P