Thunderbird on iPhone? No. There are no builds of Thunderbird for portable devices using iOS or Android. There are two possible routes that occur to me for moving your address book. One is to share your Contacts to an online address book that the iPhone can access. I don't know what service both Thunderbird and iPhone can use. Google Contacts works well between Thunderbird and Android but I suppose Apple won't touch this. Another is to put your addresses somewhere that the iPhone can get at. Can you connect the iPhone to your computer and transfer files? Or do it via a wifi or bluetooth connection? Can you swap an SD card between the two, or connect a USB drive to the iPhone? If you can, does the iPhone have any tools to allow you to import address book data? I don't use Apple, so I have no idea what they are prepared to accept. If you have any sort of account with Apple then it may be more straightforward to upload your address books via your computer to whatever it is that Apple provide. Thunderbird can export to CSV, LDIF and VCF. You're more likely to find informed answers about the import end of it at an Apple/iPhone support forum.