CAPT IN A DEP PROC IN FOREIGN AIRSPACE. ALT XING RESTR NOT MET IN CLB.

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AFTER DEPARTING MXP ON A BANKO DEP; AFTER FL100 (T ALT 6000 FT) I BEGAN MY FE DEP DUTIES AND WAS NOT ACTIVELY MONITORING THE FLT PATH OF THE ACFT UNTIL I NOTICED A DISCUSSION BTWN THE PLTS ABOUT BEING UNABLE TO CONTACT ATC (ON A NEW FREQ) DUE TO FREQ CONGESTION TO OBTAIN A HIGHER ALT. WE HAD JUST CROSSED OMETO INTXN (42 DME SRN VOR 278 DEG RADIAL) AT FL120. WE CONTINUED ON COURSE INTO THE MOUNTAINOUS TERRAIN 6000 FT BELOW THE MINIMUM XING ALT OF FL180. WE WERE ON AN IFR FLT PLAN IN VMC CONDITIONS. WE WERE 14 MI (56 DME) W OF OMETO INTXN BEFORE WE RECEIVED AN URGENT CLRNC FROM ATC TO CLB TO FL260. ATC WAS UPSET AT OUR ALT AND LOCATION AND REPEATEDLY REQUESTED OUR FLYING CONDITIONS (VMC). WE WERE FLYING THROUGH VALLEYS INTO RISING TERRAIN AND WITH TERRAIN ABOVE THE ACFT TO OUR R (5 MI?) DURING OUR SUBSEQUENT CLB TO FL260; I EXAMINED THE PLT'S BANKO DEP PAGE AND THEN REALIZED HOW LOW WE REALLY WERE ON THE DEP PROFILE. A 'NEW HIRE' CAPT WAS FLYING L SEAT ON HIS IOE. A CHK CAPT WAS FLYING IN THE R SEAT WORKING THE RADIOS. NO COMMENTS WERE MADE BY EITHER PLT AS TO WHY WE PROCEEDED W OF OMETO INTXN SO FAR BELOW THE MINIMUM XING ALT ON THE DEP PROFILE.