No, Skydeck works with your current cell phone number. When you make calls from Skydeck.com, they appear to come from that number, so that the person you are calling knows who it is and so that you don’t have to be at your desk when they call back.
Skydeck does give you a new number to dial if you want to listen to your voicemail from your phone (How do I check my voicemail?), but the people that you speak to never see that number and don’t need to know it.