Thinking about my own contacts, they're pretty evenly divided between 021 and 027, although probably slightly in favour of 021. Personally, I'm on 027 at the moment, and would like to stay with 027 at least until number portability is available.
Having said all that, it doesn't really make that much difference to me anyway, because I hardly ever use text messaging. I do have a couple of friends to prefer to communicate with text but, if they send me a text message, I tend to wait until off-peak and then phone them if I can. Generally, I find that phone and email are the only communication tools that I need.