Viber not working

Whats up with Viber. I have been using viber for a while now both in 3G and wifi without any problems. Today however in 3G it wouldnt take calls. So i uninstalled it and reinstalled it and it is still not working in 3G. I have an iphone 4... It also is not recognising the contacts on my phone that are also on Viber who I have been contacting since I originally installed it....Any ideas???

thanks