Wes Leatherock wrote in "Overlays and Dialing Plans", :
No, calls between the KS and MO sides of the Kansas City MO/KS Metro area are still local/EAS. But calls _crossing_ the state line (also now the 816/913 NPA line) _MUST_ be dialed with all ten-digits. No 1+ is required since these are still local/EAS (free) calls. This began at least ten years ago (late 1990s, IIRC).
Doing a search at Ray Chow's "Local Calling Guide" website,Kansas City KS and Kansas City MO are local to each other, and BOTH are equally/identically local to the following additional rate center exchange areas as well:
Archie MCA MO Basehor Metro KS Belton MO Blue Springs MO Bonner Springs KS Buckner MCA MO Bucyrus Metro KS Camden Point MCA MO Cleveland MCA MO De Soto Metro KS Dearborn MCA MO Drexel MCA MO East Lynne MCA MO Edgerton MCA MO Edgerton Metro KS Excelsior Springs MC MO Farley MCA MO Ferrelview MO Ferrelview MCA MO Freeman MCA MO Garden City MCA MO Gardner Metro KS Grain Valley MCA MO Greenwood MO Harrisonville MCA MO Henrietta MCA MO Holden MCA MO Holt MCA MO Kearney MCA MO Kingsville MCA MO Lake Lotawana MCA MO Lathrop MCA MO Lawson MCA MO Leavenworth Lansing MO Leavenworth Metro KS Lees Summit MO Liberty MO Linwood Metro KS Lonejack MCA MO Missouri City MCA MO Oak Grove MCA MO Odessa MCA MO Olathe KS Orrick MCA MO Osawatomie Metro KS Paola Metro KS Peculiar MCA MO Platte City MCA MO Plattsburg MCA MO Pleasant Hill MCA MO Richmond MCA MO Smithville MCA MO Spring Hill Metro KS Strasburg MCA MO Tonganoxie Metro KS Trimble MCA MO Wellington MCA MO West Cleveland Metro KS West Drexel Metro KS Weston MCA MO
I did not check to see if any of these additional KS or MO exchanges have any further local calling of their own with other KS or MO exchanges that Kansas City MO/KS does not have -- it's always possible though. I haven't checked to see about any additional exchanges in 913/KS or 816/MO though.
In July 1997, the original 913 for northern KS was split. 913 "shrunk down" to the Kansas City KS region along the eastern edge of northern KS along the border with Missouri. The rest of what was the original 913 was changed to the new 785.
In October 1997, the 816 area code in northwestern MO was split. 816 now "shrunk down" to the Kansas City MO / St.Joseph MO metro areas and corridor. The rest of what was 816 was changed to 660.
During 2000/01, it was expected that (post-1997) 816 in Missouri would soon be overlaid with the new 975 area code; similarly, 314 for St.Louis (post-1999 314/636 split, and most certainly post-1996 314/573 split) was expected to be overlaid with the new 557 area code. Neither overlay took effect at that time, nor since. The Missouri state regulatory agency kept pushing the effective overlay implementation dates later, since NeuStar NANPA was coming up with revised exhaust dates further into the future. Eventually, 314 will be overlaid with 557 for St.Louis MO, and eventually816 will be overlaid with 975 for the MO-side of Kansas City Metro as well as the corridor with St.Joseph MO.
Presently, 7D local dialing is still permissive, within 913/KS, within 816/MO, within 314/MO, even within 618/IL.10D local dialing is also permissive within 913/KS, 816/MO, 314/MO, and probably even within 618/IL. But ultimately, 10D will become mandatory for local calls within the above area codes, as 816/KS is overlaid with 660, 314/MO is overlaid with 557, and even 618/IL is overlaid with 730. But the implementation dates for the overlays and mandatory 10D is still TBD.
But local calls which cross the 913/KS 816/MO NPA/state line have been mandatory 10D since probably 1999, although these are still local/EAS calls, NOT toll calls (although there are likely certain toll corridors which also cross the KS/MO state / 913/816 NPA line).
I also tend to think that local calls between St.Louis MO in NPA 314, and East St.Louis IL & Granite City IL in NPA 618, are probably mandatory 10D these days. Also note that East St.Louis IL and Granite City IL (as well as Edgemont IL slightly further to the east, and which is local with both Granite City IL and East St.Louis IL, but NOT local with St.Louis MO), used to be Southwestern Bell NOT Illinois Bell prior to the mid-1970s! These were transferred from SW Bell to IL Bell around that time, as well as a handful of exchanges in northwest Indiana which border the Chicago IL Metro area that had been served actually by Illinois Bell were transferred to Indiana Bell. El Paso TX metro was served by Mountain Bell until around1982 when it was transferred to Southwestern Bell, although local calling still exists with nearby New Mexico (but NOT Cd.Juarez CHIH. MEXICO), so El Paso TX _never_ become part of post-divestiture US-West now Qwest.
The three exchanges in Illinois just east of St.Louis MO which had been directly served by Southwestern Bell prior to the mid-1970s -- well, SBC did buy out Ameritech (which included old Illinois Bell) around 1999/2000, and today all of it is "at&t"! Also, a large segment of south-central Illinois is part of the St.Louis MO LATA #520, and northwestern Indiana is a part of the Chicago IL Metro LATA #358. Similarly, both Illinois Bell and Indiana Bell became part of Ameritech (which was bought out by SBC, and then was later renamed "at&t").
Anyhow, more and more of the older "protected" 7D local dialing situations which cross state/NPA, or even NPA boundaries within states (or provinces) are being made mandatory 10D, but the call is still a local/EAS call. But there _are_ still several "protected" 7D local dialing arrangements that cross state/province/NPA boundaries, however, for the most part, these are in rural areas and small town areas near such state/province/NPA lines.