The SIM card memory is organized like a file system on a disk. There are
four files containing phone book entries:

Short Dial Numbers (ordinary phone book)
Fixed Numbers
Dialed Numbers
Own Numbers

You can only store one phone number in an entry. So you don't have to worry
about if it's a fax number or a mobile phone number or whatever. The length
of a file can also be zero bytes, which means that the function is not used
by the net operator/service provider. A file with Short Dial Numbers is
always present.

GSM 11.11 is the spec for the SIM-phone interface.  Section 10
details contents of the SIM's "elementary files".  The
EF-MSISDN file is the "own number" book you're looking for.
The first entry is intended for the phone's own number.

You or your carrier can put whatever you/they like in this file.
Its use and contents are entirely optional.

EF-ADN is the general SIM phonebook.

Follow http://www.3gpp.org to the specifications area to
download a copy of GSM 11.11 (there will be many "versions" to
choose from).

John

SIM cards have varying capacities depending on their size which can be
anywhere from 8k to 64k.  A 32k card typically but not always can
store 255 names and numbers.  SIM cards can generally only store names
and numbers which is different than phone memory which often can store
alternate phone numbers (work, mobile, fax, etc.) as well as other
data such as email address, web address, postal address, a note, etc.

- -