I run into many owners who want to be everything to everyone. It is no only impossible but it is an expensive venture with no return.
Small businesses can only be an Expert at so many things before they end up being mediocre. Mediocre seldom sells.
Also, to the general public, you can only have one Position in thier mind. So if you are the expert at Managed IT, it will be a stretch for you to be an expert in wireless infrastructure as well. How can someone with less than 20 employees run a network, install, maintain, train, repair, and learn Windows various flavors, UNIX, Linux, Apple/Mac, etc. In the consumer's mind, the phone company requires hundreds of thousands of employees to do one thing mediocre. So how can a company with less than 20, do so many things well?
One of the advantages of strategic partnerships (or creating different businesses for each service offering) is that you get to focus on becoming an expert in your niche, and still sell other services while delivering expertise.
Seth Godin in The Dip and the authors of Blue Ocean Strategy both discuss it in different manners. A Red Ocean is an area like voice and broadband where the prices are dropping in a blood bath between cable and telco. A Red Ocean would be Luxe, a cell company that charges $500 per month.
Planning and Focus (Or Concentration) are key to Execution.