If you mean by PCO as cell phone, there are a number of them that can handle email.

I mean a PCO (public call office) or a public telephone.

I think what makes this idea only average is that cellphones have pretty much become ubiquitous and cheap enough that a 12yold can own one and throw away 6-months later...virutally all cellphones come with email and instant messaging activity...having access to a public landline phone w/ email access wouldnt be all that necessary...though sometimes it might come handy, but i dont think it will be worth Bell/AT&T's time to set up systems that did that nationwide..maybe in a few malls but once again, since everyone has cellphones its not necessary