Have always used cat 3 jacks for phone and cat 5 for data. I like to keep to standards. We run blue cat 5 for data and white for telco. The telco wires get punched to a 110 telco hub and the data gets punched to a 110 data hub. If putting an RJ11 in an RJ45 jack, the pins have too much play which could create issues. You would have to make up a tail like Stamp suggested.The customer at some point will try to stick an ethernet cable into it and wonder why he can't get on line. Using the industry standard eliminates those phone calls. As Ernie mentioned, there is ring voltage on a telco line.....it could damage a computer potentially....... If the glove dont fit......the customer can't plug in

Telco is the least of my worries on any given project so I keep to industry standards.