AIR TAXI PLT OF A B234 HAS NMAC WITH A TWIN CESSNA WHEN CLRED ON BASE AND READY TO TURN FINAL. NO TIME FOR EVASIVE ACTION.

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APCHING ARPT FROM NE TO LAND; ATIS ADVISED RWYS 25 IN USE. ARRS FROM THE N TO CONTACT THE TWR ON 120.2 FOR RWY 25R; FROM THE S 118.4 FOR RWY 25L. I WAS ON FLT FOLLOWING WITH PHX APCH (120.7) AND WAS HANDED OFF TO THE DVT TWR ON 118.4; WHICH CAUSED ME TO WONDER WHY NOT 120.2 PER THE ATIS (SURPRISE #1). TWR REQUESTED A POS RPT OVER 'CAVE CREEK DAM' ON A R BASE. I RPTED 'CAVE CREEK DAM' AND REQUESTED RWY 25L. TWR CLRED ME TO LAND RWY 25R WITHOUT SWITCHING ME TO 120.2 (SURPRISE #2). ABOUT 30 SECONDS LATER; TWR CLRED ME TO CONTINUE FOR RWY 25L. I SLOWED TO 120 MPH; MAINTAINED 2500 FT MSL; AND LEFT THE GEAR RETRACTED SINCE MY BASE LEG WAS ABOUT 1.5 MI E OF THE ARPT. NEAR THE POINT TO START THE TURN TO FINAL; I WAS ABOUT TO KEY THE MIKE TO REQUEST A LNDG CLRNC WHEN A TWIN CESSNA CAME OUT FROM BEHIND MY WINDSHIELD POST (SURPRISE #3) ON A STRAIGHT IN FOR RWY 25L. THE CESSNA WAS ABOUT 200 FT BELOW ME AND DSNDING WITH THE GEAR DOWN SO NO EVASIVE ACTION WAS REQUIRED OR TAKEN. WITH THE HAZE AND LOW SUN ANGLE; IT IS VERY UNLIKELY THE CESSNA PLT(S) EVER SAW MY AIRPLANE. THE TWR INDICATED THEY DID NOT KNOW I WAS ON A R BASE FOR RWY 25L AND CLRED ME TO LAND RWY 25R (SURPRISE #4). SURPRISED BECAUSE I HAVE GONE INTO AND OUT OF PHX SKY HARBOR OVER 1000 TIMES AND THEY CONSISTENTLY USE ONLY ONE FREQ PER EACH RWY. CONTRIBUTING FACTORS: 1) I WAS NOT LOOKING FOR TFC ON A STRAIGHT IN AS THE ONLY TFC I WAS AWARE OF WAS THE TFC PHX APCH CALLED OUT SEVERAL TIMES. SUBJECT TFC WAS RPTED 3 O'CLOCK POS AND 3 MI ON EACH CALL. I DON'T RECALL THE ALT RPTED; BUT DEDUCED WE WERE CLOSE TO PARALLEL COURSES AND SPD. THERE WAS NO CLUE AS TO DEST; BUT I HAD CONCLUDED I WOULD ARRIVE WELL AHEAD OF THE SUBJECT TFC IF ITS DEST WAS DVT. 2) FREQ CONGESTION IS DEFINITELY A CONTRIBUTING FACTOR. I DID NOT CORRECT PHX APCH ON THE DVT TWR FREQ ASSIGNED OR ASK WHY I WAS GIVEN A FREQ DIFFERENT THAN THE ATIS BECAUSE I DIDN'T WANT TO CONGEST THE BUSY FREQ WHEN IT SEEMED TO BE UNNECESSARY. SOMETIMES IT HAS TAKEN SEVERAL MINS TO CORRECT ONE SIMPLE SLIP OF THE TONGUE. THERE ARE A LOT OF CASES WHERE TWO OR MORE TRANSMITTERS ARE IN USE AT THE SAME TIME; OR THE FIRST OR LAST PART OF A XMISSION IS CLIPPED OFF BY IMPROPER USE OF THE MIKE BUTTON. I BELIEVE ACFT RECEIVE UNREADABLE XMISSIONS CAUSED BY INTERFERENCE GND RECEIVERS NEVER HEAR. FOR INSTANCE; AN AIRPLANE ON THE GND 25 MI AWAY INADVERTENTLY XMITTING ON A TWR OR APCH FREQ. RADIO COMS APPEARS TO BE THE WEAKEST LINK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HIS ACFT WAS BE36 AND THE CTLR MAY HAVE GIVEN HIM THE CLRNC FOR THE TWIN TO LAND ON THE L. HE DID NOT MIND THE IDEA SINCE IT WOULD HAVE SAVED HIM A LONG TAXI IN THE 115 DEG TEMP. IT IS HIS BELIEF THAT THE ACFT CALLED AS TFC WAS HEADING TO SDL ARPT. THIS IS A CITY OPERATED TWR AND RPTR BELIEVES THE TRAINING IS NOT UP TO STANDARD.