EMB ERJ 170/175 ER/LR
Confusion; Communication Breakdown; Distraction
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Procedure
We were initially cleared for take off by Tower Control to depart Runway 23 from CLT and fly the JACAL 6 RNAV departure procedure.  Shortly after checking in with Departure Control the Controller gave us a 300 heading direct and cleared us direct to a fix.  The Captain and I were confused by the pronunciation of the fix; we thought to be VLADY.  I asked the Controller to clarify and confirm direct to VLADY; which she did.  Shortly there after the Controller stated that we were showing north of the fix and cleared us direct to JACAL.  Upon further investigation we determined the Controller wanted us direct to GLADI a fix on the departure procedure and not VLADY a fix a little further down on our flight plan. Short cuts are great; but flying RNAV SID's as depicted allow pilots to fly what they brief.  The Controller was working another frequency at the time and was issuing an IFR clearance to an aircraft.  The division of attention my have lead to the Controller not fully hear my verbalization of VLADY.  Also having two fixes close to each other with similar names can lead to confusion and is not a good idea.
This was a simple case of misinterpreted instructions with two points that sounded very much alike; and which were both on our route of flight. The First Officer and I both thought we were getting an early morning shortcut and the Controller noticed our deviation quickly and issued an updated clearance. Repeat points by spelling them out phonetically whenever in doubt.
An ERJ170 on the CLT JACAL 6 RNAV departure was cleared to GLADI intersection but misunderstood and proceeded to VLADI intersection which was a more distant point on their flight plan. This was a similar sounding fix confusion.