I explain to customers that in almost all advertisements you assume that you want your elements, the logo, contact information, imagery, services, etc... to all work "2Gether"
. However, in reality they are all competing for people's attention. Every element you add weakens the strength of every other element. One or two things to display is easier for the audience to absorb than 15 different things.
It's difficult for folks to not look at something like vehicle wrap as they would a business card. They assume that all of the elements they have on a business card are extremely important. But they are two entirely different forms of advertisements that play different roles. On something like a vehicle, and this is mostly true for all outdoor adverting, you only have a few seconds to say what you need to say. So it's our job as designers and sign makers to help our clients figure out what is the most important message to present. Then you really should focus on that one message, everything else should support that one message.
A hook is important but that hook should really be a part of the logo or brand. A well designed logo should draw a person in and explain to viewers what type of business it is. If it doesn't, you are then needing to create an extra element to compete with that brand, just to explain what the brand is. There isn't enough time to do that on an outdoor advertisement.
So how many elements are on your design? Is it possible to remove elements that may be important but not as important as the main message? I think the most successful wrap designs serve one main purpose: to promote brand recognition.
And they are right about phone numbers. A phone number may be important, but is it as necessary as promoting a brand? It's a well known fact that people cannot remember a series of 7 -10 numbers for more than a moment. So in most cases that phone number is simply taking up space and distracting people from remembering the name. If they cannot remember the name, and I bet you money they cannot remember a phone number, how are they going to find you when they do need to hire you, because it is extremely rare that someone sees an add with a phone number for something like a service and decides that they need to hire that company right then and there. So how can you expect that they will remember a number, or even write it down and keep it for more than a day. It's much more common that they remember a name of a business, and when they do need to hire that business, they will look it up online, in the phone book, etc...
I think a better strategy for displaying contact information on an outdoor advertisement, is to own a domain that is the exact same thing as the company name. Then when they are remembering your contact information, your web address, the are also remembering your companies name at the same time. Really it's only one thing for them to remember.
Also if you or a client absolutely insists that multiple elements need to be on a design. Use size, space and contrast accordingly to play favorites. In your case I would promote the name of the business more than the list of services you offer. That may require that you fuss with your logo or brand a bit so that it somehow explains who you are. But that way you won't have to make your laundry list of services the focus. What's the point of knowing all the services you offer if they miss your logo and name. You know what I mean?