A CLBING B737-200 FLC EXCEEDS THE 250 KT SPD LIMIT BELOW 10000 FT AFTER THEY RECEIVE A RELEASE FROM ANY SPD RESTRS FROM DEP CTLR AT IAH; TX.

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FLT FROM IAH (HOUSTON) TO PHX (PHOENIX) DEPARTED RWY 15L AND CONTACTED HOUSTON DEP CTL ON 123.8. THE FLT WAS INSTRUCTED TO TURN TO A 250 DEG HDG AND CLB AND MAINTAIN 5000 FT. SHORTLY AFTER THIS HOUSTON DEP CTL ASSIGNED 290 DEG HDG TO JOIN J86 AND A CLB TO 15000 FT. ALSO HOUSTON DEP ASSIGNED US A NO SPD LIMIT INSTRUCTION AFTER THE AIRPLANE HAD CLBED THROUGH 5000 FT. I TOLD THE CAPT THAT I RECALL THAT OUR UNION RECOMMENDED US NOT TO ACCEPT ANY NO SPD LIMIT CLRNC WHEN DEPARTING HOUSTON CLASS B AIRSPACE. THE CAPT SAID THAT SINCE HOUSTON DEP HAD ASSIGNED US A NO SPD LIMIT CLRNC AFTER LEAVING 5000 FT; THAT HE WOULD COMPLY WITH IT AFTER WE HAD CLBED ABOVE SOME CLOUDS. SO I TOLD HOUSTON DEP THAT WE WOULD KEEP THE SPD AT 250 KTS IN THE CLB UNTIL WE WERE ABOVE SOME CLOUDS. ONCE ON TOP OF THE CLOUDS AT ABOUT 6500 FT; THEN TOLD HOUSTON DEP THAT WE COULD ACCELERATE TO THE NO SPD LIMIT CLRNC THAT THEY HAD ASSIGNED. HOUSTON DEP ASSIGNED THE NO SPD LIMIT CLRNC TO US WHEN DEPARTING THEIR CLASS B AIRSPACE; SO I GUESS THE PROC IS STILL AUTH. HOWEVER; I FEEL THAT A NO SPD LIMIT AUTH COULD BE UNSAFE IN A HIGH VOLUME TFC CLASS B AIRSPACE.