CPR SMT ALT DEVIATION OVERSHOT AND FREQ CHANGE WRONG LEAVING MDW.

Narrative

FLT WAS FROM MDW TO DUPAGE ARPT. CLRNC WAS RECEIVED AS FILED INCLUDING MDW 3 DEP SID. MDW 3 INCLUDES MAINTAIN 3000' AFTER DEP. GND CTL CLRED US TO RWY 4L WITH NEW DEP FREQ. BOTH THE COCAPT AND MYSELF UNDERSTOOD 'MAINTAIN 4000'.' I QUESTIONED THE CLRNC TO TAXI TO RWY 4L WHICH WOULD MEAN XING AN ACTIVE RWY. GND CTL ACKNOWLEDGED RWY 4R INSTEAD OF RWY 4L. AFTER TKOF WE CONTACTED DEP. WE WERE TOLD WRONG FREQ; SHOULD BE ON XXXXX. WE SWITCHED TO WHAT WE FELT SHOULD HAVE BEEN THE PROPER FREQ ALSO GIVEN BY CLRNC DEL. MEANWHILE; WE WERE CLBING TO 4000'. AT 3800' DEP REQUESTED OUR ALT. HE WAS ADVISED 3800' CLBING TO 4000' AS CLRED. DEP ASKED US TO DSND IMMEDIATELY TO 3000' AND THAT HE WOULD CONTACT MDW TO DETERMINE WHY 4000' WAS ASSIGNED. WE ALSO CONTACTED MDW AND WERE ADVISED THE CLRNC WAS TO MAINTAIN 3000' AS PER THE SID BUT EXPECT 4000'. AFTER NUMEROUS PHONE CALLS TO MDW WE FAILED TO GET ANYONE TO LISTEN TO THE TAPE. 5/88; MGR ORD ATC TWR ISSUED A LETTER TO AIRMEN BLAMING THEM FOR SERIOUS SITUATIONS CAUSED BY SOME PLTS. HIS MAIN SUBJECT WAS WRONG FREQS (COPY OF LETTER ENCLOSED). THE COCAPT AND I RECOGNIZED THE WRONG RWY ASSIGNMENT. WE UTILIZED THE WRONG GIVEN FREQ AFTER TKOF AND CLBED INTO A POTENTIALLY DANGEROUS SITUATION. LESSONS TO BE LEARNED: PAY CLOSE ATTN TO CLRNCS; QUESTION UNUSUAL CLRNCS THAT DEVIATE FROM A GIVEN SID; PLTS AND CTLRS CAN MAKE MISTAKE; AND LAST AND CERTAINLY THE MAIN CONCERN IS BE ALERT!