The Lewis Principle
Originally only US phones had letters associated with numbers, because we hit the need for 7 digit numbers first and mnemonic devices were used (7 digit NNN-NNNN was considered too much to memorize so they did LLL-NNNN). No letters were associated with 1 for technical reasons, nor with 0 (zero), which was reserved still for operator in places other than hotels. The mnemonics were like TREmont-8264, so Q and Z were left out leaving numbers 2-9 three letters each.
When alpha became vogue for other reasons, competing telephone manufacurers around the world came up with different solutions for integrating Q and Z (how else can you market 1-800-ANTIQUE?). Many had the bright idea to put them on the 1 key (no longer a technical obstical, while 0 still meant operator). When it came time to find a global solution, fights ensued because nobody likes to change, or to lose. In the UK, oddly, the O and Q were put to the O (matching shapes?) and the Z was still ignored.
Steve Lewis, leading the IA team at Bell Labs, went to bat for reason and sanity, going to Geneva for an international standards meeting. His argument? The alphabet should go in alphabetic order. Who can argue with that?