The iPhone Dev-Team has issued an update to the UltraSn0w unlock which fixes the disappearing carrier name issue.

UltraSn0w .92 was posted by MuscleNerd and uses an extra 10 lines of code to fix the carrier name. It is available on the normal repo666.ultrasn0w.com Cydia repository.

You can find instructions on how to unlock your iPhone using UltraSn0w. Remember to use UltraSn0w you must be on the 04.26.08 baseband.

[Update]: The carrier fix has been confirmed for: USA, Thailand, Austria, Trinidad, Germany, China, Kuwait, Serbia, Poland, France, Nigeria, Egypt, Pakistan, Ireland, UK, Turkey, Sweden, Switzerland, Malaysia, Hungary, The Netherlands, Bahamas, Jamaica, India, Israel, Belgium, Canada, Portugal