Few weeks ago, my smartphone died. Someone lent me an old Nokia phone (6021) and I was looking for a way to send all my contacts and phone numbers to it.
The Nokia phone supports Bluetooth connectivity and seems to understand the vCard standard (rfc6350). All contacts can be exported as vCard file using Mozilla Thunderbird "Export" features in Address Book.
We will see that Nokia phone does not follow the vCard standard and we will need to hack the vCard information to be understandable by the phone. I use Python with module vobject to do that.