MLG USES WRONG FREQ FOR DEP AND ENTERS ATA FOR NEARBY AFB.

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OUR ACFT WAS A SHORT-RANGE B737-300 AND DUE TO WT LIMITATIONS COULD ONLY USE RWYS 1R OR 7R AGAINST NORMAL TFC FLOW. WIND WAS CALM. THE TWR GAVE US RWY 1R AS IT WOULD BE THE QUICKEST (LEAST AMOUNT OF TFC). THE OVETO SID CALLED FOR A TURN TO 070 DEGS AT 2 DME (LAS VOR) AND NO CLB RESTRS. THE CLRNC WAS UP TO 17000 FT WITH DEP FREQ OF 133.95. I WAS THE FO AND PF. AS WE WERE CLRED FOR TKOF; I SHUT THE ENG BLEEDS AND SET MAX PWR. ABOUT HALFWAY IN THE TKOF ROLL THE TWR GAVE US 3 NEW ITEMS; 'FLY RWY HDG; MAINTAIN 7000 FT; NEW DEP FREQ IS 118.4.' THE CAPT (PNF) SET HDG AND ALT ON THE FLT MGMNT PANEL; WHICH I VERIFIED; BUT I DIDN'T LOOK DOWN TO SEE HIM TUNE THE RADIO AS I WAS BUSY WITH ROTATING THE HVY ACFT. THE CAPT CALLED DEP AS WE CONTINUED TO THE N OF LAS. SOMEONE ANSWERED BUT SEEMED RATHER VAGUE. AFTER BEING CALLED AGAIN; WE WERE ASKED OUR POS. AFTER WE TOLD THEN; WE WERE GIVEN AN IMMEDIATE R TURN TO 080 DEGS AND NEW FREQ OF 118.4. WE BOTH CHKED AND 119.4 HAD BEEN INADVERTENTLY SET ON THE VHF. WE MAY HAVE ENCROACHED ON NELLIS AFB'S TFC AREA. TOO MANY ITEMS GIVEN BY THE TWR AT EXACTLY THE BUSIEST POSSIBLE TIME.