Looking for 4 line phone for small business

I am looking for a desktop phone that can handle 4 phone lines. We are a small company engine repair company currently with 4 phones running on 3 phone lines. I've done a lot of searching online and have tried a couple at Staples. Most seem to be proprietary and only work properly with a couple other models from the same brand. Some beep constantly every 2 seconds when you put someone on old ( the customer hears the beeps ), which can be quite annoying.



Does anyone have knowledge of a good place to look or models to look at?



Appreciated, Ryan