File Extension I01 File Format Winphone phonebook I01 stands for Winphone phonebook. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question How to remove the two unnecessary Desktop in Blackberry Phonebook Option? The last two records in subfile are same...if i delete that also it is taking last record and showing in display two times.. Tricky Grouping problem!