This isn't even a suggestion,
it's an annoyance you have with people who don't have msn on their computers. Frankly a lot of people don't want to use msn because then they have to listen to all your chit chat for hours on end before and after the trade, the PM system works fine for setting up trades, and if not then there is always this wonderful tool called IRC, if anything this should be posted on a guide or something and elaborated upon a lot more.
Ie guide title could be "What to do if you don't have msn?"
and then you could go on to list several ways to complete the trade without it. I personally only have msn and don't want to use AIM, but many people only have AIM, what do I do? Do i go make an AIM account for that one person I want to trade with who has AIM? No I use IRC, simple.
My two cents as usual.
Thanatos.