Facebook is forcing use of its new messenger app, which is only supported on iOS7?
The mobile site will still allow you to send/receive messages in Safari and other browsers. It may also be that the version of the app you are using is so old that they cannot prevent the messenging functionality from working; you'll have to wait to see about that or dig up user comments on the topic from Europe, which was pushed into this model in the spring. 

Considering that the public's response to this news has been almost uniformly negative, I think it's reasonable to suspect that this policy change may be reversed after the numbers are crunched and usage declines become obvious. The primary point of splitting the apps is to increase revenue by doubling the ads the users are forced to see; if people stop using the original app and refuse to download the messenger app, this plan backfires.