B737-300 CREW HAD A GPWS 'TERRAIN' WARNING; AT THE SAME TIME THE APCH CTLR ADVISED THEM THEY WERE TOO LOW.

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WHILE CAPT WAS TRYING TO CALL COMPANY OPS FOR GATE ASSIGNMENT (ACFT AT 14000 FT AND ABOUT 40-50 MI FROM ARPT); FO RESPONDED TO THE APCH CLRNC HE THOUGHT WAS TO DSND TO 10000 FT FROM 14000 FT. AT ABOUT 25 MI FROM TUS; APCH CTL TOLD CREW THEY SHOULD BE AT 11000 FT. AS FO STARTED AN IMMEDIATE CLB; THE GPWS GAVE ONE 'TERRAIN' CALL. THE CTLR CLRED US TO 6000 FT ABOUT 1 MIN AFTER REACHING 11000 FT. ALTHOUGH THE CREW WAS FATIGUED FROM A LONG DAY; A POTENTIAL PROB ALWAYS EXISTS WHEN ONE (PF) IS DOING THE FLYING AND ATC RADIO WORK; WHILE THE PNF IS USING ANOTHER RADIO. MUCH OF THIS PROB IS ELIMINATED ON THE NEW GENERATION ACFT WHERE INFO; SUCH AS GATE ASSIGNMENTS; ARE RECEIVED WELL IN ADVANCE BY ELECTRONIC ACARS. SUPPLEMENTAL INFO FROM ACN 578112: APPROX 25 MI E OF TUS; CAPT WAS ON #2 RADIO TALKING TO COMPANY. RECEIVED CLRNC FROM APCH CTL TO DSND TO WHAT I THOUGHT WAS 10000 FT. READ BACK CLRNC AS 'CLRED TO 10000 FT.' SET IN ALT AND ADVISED CAPT WHEN HE RETURNED TO FREQ. WORKLOAD GOT HIGH AS WE REQUESTED RWY 29R INSTEAD OF RWY 11L. I WAS WORRIED I WOULD BE TOO HIGH ON APCH -- COMPANY PAGE HAD NOTE REGARDING HIGH/UNSTABLE APCHS DUE TO TERRAIN E OF ARPT. ABOUT THAT TIME; APCH CTL QUERIED US ON ALT; AND SAID WE WERE SUPPOSED TO BE AT 11000 FT. WE RECEIVED GPWS TERRAIN WARNING. RECEIVED ONLY 1 'TERRAIN; TERRAIN' AURAL WARNING. I LOOKED AT RADAR ALTIMETER AND DID NOT NOTE ANY INDICATION. STARTED IMMEDIATE CLB TO 11000 FT; AND COMPLIED WITH TURN TO HDG ASSIGNED BY APCH CTL. SHORTLY THEREAFTER; CLRED TO 6000 FT. LATER CLRED FOR VISUAL APCH AND LANDED WITHOUT FURTHER INCIDENT. IN RETROSPECT; SHOULD HAVE BEEN MORE AWARE OF TERRAIN HEIGHT (MINIMUM SAFE ALTS ON APCH PLATE) AND QUERIED CLRNC TO 10000 FT. WOULD HELP TO HAVE DIGITAL ATIS INFO AND ABILITY TO GIVE COMPANY INFO THROUGH ACARS SO THAT MONITORING PLT IS NOT OFF FREQ.