The sudden ban on Twitter by Pakistan because it was not agreeing to delete objectionable material connected to Prophet Mohammad has subsequently been reviewed and normalcy has been restored as reported in The Australian dated 21st of May 2012.
The blocking of Twitter in Pakistan was carried out by the telecom authority based on orders of the IT Ministry because Twitter was refusing to delete posts which carried caricatures of the Prophet and contained blasphemous material which hurt the sentiments of Muslims.
It seems Facebook had deleted the posts but not Twitter.
However, the ban is withdrawn after 12-hours and normalcy has been restored.
Twitter is a fantastic medium to keep in touch with others and for sharing information and is used by celebrities and prominent public figures like Pervez Mushararf,, and Ali Zafar.