"E" is Eastern Time Zone, "C" is Central Time Zone, "M" is Mountain Time Zone, and "P" is Pacific Time Zone. Occasionally, an area code will fall in more than one time zone. In this case, the abbreviation is a combination of the previous abbreviations. Some area codes are shown with time zones referencing Universal Coordinated Time (UTC).
Additional technical status can be retrived from the North American Numbering Plan Administration on the 501 area code specific link here.
Area code 501 went live into service on January 01, 1947 (The paperwork process started on January 01, 1947).  This area code was split to create the 870 area code(s).
Redfield (72132), Kearney (72132), Orion (72132), Bradford (72020), Little Rock (72211), Searcy (72143), Georgetown (72143), Jessieville (71949), Buckville (71949), Beaudry (71949), Conway (72032), Beryl (72032), Brumley (72032), Central Baptist College (72032), Gleason (72032), Gold Creek (72032), Gold Lake Estates (72032), Preston (72032), Saltillo (72032), Skunkhollow (72032), Heber Springs (72543), Eden Isle (72543), Morrilton (72110), Oppelo (72110), Dabney (72110), Hickory Hill (72110), Lanty (72110), Lewisburg (72110), Riverview (72110), Sandtown (72110), Wesley Chapel (72110), El Dorado (71730), Alexander (72002), Little Rock (72212), Wrightsville (72183), Malvern (72104), Rockport (72104), Brown Springs (72104), Butterfield (72104), Durian (72104), Gifford (72104), Glen Rose (72104), Magnet Cove (72104), Perla (72104), Rolla (72104), Social Hill (72104), Beebe (72012), Casa (72025), Divide (72025), Homewood (72025), Pontoon (72025), Round Mountain (72025), Jones Mill (72105), Jacksonville (72076), Gravel Ridge (72076), Little Rock Afb (72076), Lr Afb (72076), Lrafb (72076), Air Base (72076), Jax (72076), Lr Airforce Base (72076), Macon (72076), Benton (72015), Bryant (72015), Haskell (72015), Tull (72015), Clinton (72031), Alread (72031), Botkinburg (72031), Crabtree (72031), Culpeper (72031), Formosa (72031), Koch Ridge (72031), Plant (72031), Rex (72031), Rupert (72031), Walnut Grove (72031), Cabot (72023), Little Rock (72206), Hot Springs National Park (71901), Fountain Lake (71901), Hot Springs (71901), Blue Springs (71901), Central City (71901), Euclid Heights (71901), H Spg Nat Pk (71901), Hot Springs National (71901), Hs (71901), Lakeside (71901), Mountain Valley (71901), Mt Valley (71901), Oaklawn (71901), Ozark Lithia (71901), Piney (71901), Pleasant Hill (71901), Price (71901), Red Oak (71901), Little Rock (72205), Lonoke (72086), Bayou Metro (72086), Furlow (72086), Pettus (72086), Wattensaw (72086), England (72046), Greenbrier (72058), Linder (72058), Mcgintytown (72058), Pleasant Valley (72058), Republican (72058), Springhill (72058), Bald Knob (72010), Judsonia (72081), Steprock (72081), Providence (72081), Kensett (72082), Kenseh (72082), Kensen (72082), Griffithville (72060), Bigelow (72016), Perryville (72126), Aplin (72126), Cherry Hill (72126), Deberrie (72126), Nimrod (72126), Thornburg (72126), Williams Junction (72126), Damascus (72039), Twin Groves (72039), Gravesville (72039), Martinville (72039), Pleasant Plains (72568), Pleasant Plns (72568), Donaldson (71941), Saginaw (71941), Center Ridge (72027), Catholic Point (72027), Lick Mountain (72027), Middleton (72027), Little Rock (72209), Mc Rae (72102), Mcrae (72102), Marshall (72650), Canaan (72650), Dongola (72650), Landis (72650), Wheatley (72392), Mayflower (72106), Lollie (72106), Maumelle (72118), North Little Rock (72118), N Little Rock (72118), Nlr (72118), No Little Rock (72118), N L R (72118), N Lr (72118), Blue Hill (72118), Crystal Hill (72118), Jeffery (72118), West Marche (72118), Scott (72142), Hamiter (72142), Kerr (72142), Toltec (72142), Rose Bud (72137), Sidon (72137), Bauxite (72011), Quitman (72131), Enders (72131), Fairbanks (72131), Pearson (72131), Scotland (72141), Paron (72122), Star City (71667), Cornerville (71667), Crigler (71667), Glendale (71667), Griffith Spring (71667), Nebo (71667), Palmyra (71667), Relfs Bluff (71667), Tarry (71667), Bee Branch (72013), Perry (72125), Cleveland (72030), Beverage Town (72030), Shirley (72153), Eglantine (72153), Lexington (72153), Rushing (72153), Pangburn (72121), Davenport (72121), Dewey (72121), Hickory Flat (72121), Little Red (72121), Mcjester (72121), Vilonia (72173), Holland (72173), Naylor (72173), Otto (72173), Bismarck (71929), Lambert (71929), Little Rock (72223), North Little Rock (72116), N Little Rock (72116), Nlr (72116), No Little Rock (72116), N L R (72116), N Lr (72116), Enola (72047), Barney (72047), Fairfield Bay (72088), Shirley (72088), Lonsdale (72087), Owensville (72087), Little Rock Air Force Base (72099)