And the reason why people were defaulting to MSN Messenger was... Because SMS weren't free. The same thing was happening in the USA/Canada at that point in time, nothing exceptional about Europe. Free SMS reversed that trend in one place, the change to phone plans didn't happen quickly enough in the other place and a third party app won, that's all.
What's nice about SMS is that it will always work as soon as there's a signal and no matter what phone people have, no need to install multiple third party apps to cater to the needs of those who decide to go against the flow and use something else, you boot your phone for the first time and it's ready to send messages no matter the phone, simple as that.