B90 CREW ASSIGNED 2000 FT ON DEP FROM NEW ARPT CLB TO 3000 FT AND INSTRUCTED TO RETURN TO 2000 FT FOR TFC.

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AUG/MON/01; AT ABOUT XA20; WE DEPARTED ZZZ1 ENRTE TO ZZZ2 ON AN AIR AMBULANCE FLT. THE IFR CLRNC WE RECEIVED WAS PREDICATED ON A S DEP; BUT THE DEP RWY WAS CHANGED TO RWY 36L. I WAS THE PF WHILE THE COPLT HANDLED THE COM. INITIAL INSTRUCTIONS WERE CLB TO 2000 FT ON RWY HEADING AND EXPECT 14000 FT IN 10 MINS. AFTER CONTACTING DEP; WE WERE INSTRUCTED TO TURN L TO 250 DEGS WHICH WOULD PUT US IN CLOSE PROX TO ZZZ APCH COURSE. ANTICIPATING THE USUAL CLB CLRNC TO AN INTERMEDIATE ALT; I CLBED THROUGH 2000 FT AND WAS AT 3500 FT WHEN THE CTLR QUESTIONED MY ALT. AFTER CONFIRMING THE ACFT ALT; I WAS INSTRUCTED TO RETURN TO 2000 FT. AN AIRLINER ON APCH TO RWY 19 AT ZZZ WAS HELD AT 3500 FT. AFTER COMPLYING WITH ATC AND W OF ZZZ; I WAS INSTRUCTED TO CLB AND CHANGE FREQS. I ATTRIBUTE THE INCIDENT TO ANTICIPATING THE USUAL CLB INSTRUCTIONS TO AN INTERMEDIATE ALT WITHOUT VERIFYING. A CONTRIBUTING FACTOR WAS THE INTERCOM MUTES THE VOICE WHEN 1 PLT IS XMITTING; THEREBY PREVENTING BOTH PLTS FROM MONITORING ATC COMS. I HAD NEVER RECEIVED AN ALT RESTR THIS LOW (2000 FT) PRIOR TO THIS INCIDENT AND IT REINFORCES THE NEED TO CONFIRM CLRNCS WHENEVER ANY DOUBT EXISTS AND TO BEWARE OF ASSUMPTIONS BASED ON PAST EXPERIENCES.