1: SIM cards can only take a limited number of phone numbers (not contacts), maybe 100, maybe 200 (depending on SIM card).
2: And those are numbers, not contacts: Each entry is one name (not too long), and one number.

If you want a proper transfer of contacts, then dump the contacts list through bluetooth or something. I can send a list from any of the older phones I have, to either my N800 or a laptop with bluetooth, and I end up with a .vcard file with all the contacts. This contacts list can be ingested or massaged back into a new device. If you try to do this via the very limited phone number list on a SIM card you will lose information unless your contacts list is really just a phone number list, and short.