Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented
Human Factors
SGF ramp is a power out ramp versus a pushback.  After starting both engines and doing the after start checklist; the capt asked to call for  taxi clearance.  As I was doing this; he released the parking brake and starting to power up.  The mechanic came on and said 'I'm still down  here'.  The capt stopped immediately and apologized profusely.  The mechanic said it was not a problem and signed off.  The marshaller  guided us out and we departed uneventful. This was just us not paying close enough attention.  When we are pushed back; we are used to hearing pushback crew say their 'speech'  about the pins and tug.  Of course we didn't hear this as it was a power out.  I guess it just threw us off.  No excuse for it; it just happened.  It sounds cliche but we just needed to pay better attention.  The capt felt horrible about it.  I don't think we rolled more than a foot or two but it  could've been bad had the mechanic not been paying attention.  I as FO will try and be better backup and consciously slow things down when  things aren't going 'according to script'.
Air Cargo First Officer describes an attempt to taxi out of the parking spot; forgetting that the Mechanic is still below the aircraft on the headset; waiting for the 'cleared to disconnect' command. The aircraft is quickly stopped and no injuries occur.