To open facebook page in facebook app you should:
1)Find uid of your page (it can be done for example by looking at source code of your facebook page)
I got the following fragment from the source code of the page: http://www.facebook.com/yourpage
{"text":"yourpage","type":"ent:page","uid":****123****}
N.B.: To check if uid is correct substitute uid for pagename: http://www.facebook.com/****123****
This url should open your page.
2) When the uid is found and is correct use this code:
NSURL *urlApp = [NSURL URLWithString:@"fb://profile/****123****"];
[[UIApplication sharedApplication] openURL:urlApp];
This code will open you page within facebook app. N.B.: Do not forget to check if the facebook app exists( or more precisely that the url can be opened) using: if ([[UIApplication sharedApplication] canOpenURL:urlApp])
otherwise open it in Safari.