There were all kinds of plans in all kinds of cities. Dallas and Houston at one time had 1L-4D numbers (Riverside-4085 in Dallas, for example, was R-4085).. Oklahoma City had 5D and 6D numbers, later changing to 2L-4D. Tulsa at one time had a mixture of 4D, 5D and 6D numbers, all at the same time. It all depended on the circumstances and the history of the numbering plan, growth, expansion of the dialing area, contiguious tiers, and others facts, not least of which was the engieners and the traffic engineers preferences, along with the preferences of higher managers.
The president (the title then meant CEO) of Southwestern Bell agreed to allow Wichita Falls, Texas, to be the guinea pig for ANC (all-number calling, that is, 7D). The reaction was so adverse that he declared no other SWBT city would go ANC during his tenure as CEO (quite a few more years), and none di.
Eventually, of course, all changed to 2L-5D or directly to 7D.
Wes Leatherock snipped-for-privacy@aol.com