There is no direct way to transfer messages from blackberry to iphone. Maybe you should try these.

1 Backup your blackberry data with BB Destop software on computer. Data will be saved as a bbb file.

2 Use some BBB to CSV converter program to export messages from backup file to a CSV file.

3 Contacts a program vendor called Backuptrans to extract messages from CSV file to a Backuptans database file.

4 Transfer messages from database file to your iPhone using the program Backuptrans iPhone SMS Transfer.

5 Restart your iPhone then you will see your messages there in Messaging on iPhone.

Hope this can help.