[soperj]

yeah, I guess you'd start with the first 13/last 13 and break it down in halves from there. It would take only 6 choices to pick a letter. I still think memorizing the binary version of the letters would be faster, and wouldn't take all that long considering the amount of use.

[dn3500]

The code is (or can be) the same either way. I imagine after a few days the user would memorize the codes for the letters and skip the prompts.

On a related note, one character per minute is about the same speed as the first trans-atlantic telegraph cable in 1858.

[DarylZero]

You want a variable length code that takes into account letter frequencies.