I’ve been investigating copying contacts from Outlook to the Siemens C475 IP phone. It is possible! The contacts need to be in a .vcf format in order to be imported into the phone. Save it to your PC and then open it using Notepad (or any other text reader) and you can see the information it needs for each contact to be moved to the phone. If you have a lot of contacts in Outlook then there appear to be some pieces of software you can try/buy to export the contacts to one .vcf file (apparently this is commonly needed when people migrate their contacts from a PC to a Mac).
Having got the .vcf file you then login to your Siemens phone through the browser (you can find the IP address from the handset by clicking menu > settings > base > local network) and click to Settings then Handsets. Then click which handset you want to copy the contacts to (i.e. INT 1 or INT 2) and in the Transfer directory to handset box browse to the .vcf file and then click Transfer. You can then do the same for the other handset.
I have attached an example .vcf file that works with the Siemens C475 IP: teledir.vcf
