The IMSI hex challenge

I'm trying to read the IMSI numbers from several Nokia DCT-4 Partial
flash files.

On some models, the IMSI is shown in decimal but on most it is in a
weird hex format.
I've done some testing and established a pattern confirming that what
I'm looking at is the IMSI, but I'm out of ideas about how Nokia have
encoded it.

Some examples are (these are not live IMSI's btw)

?23415903125xxxx = EC0E465116DE0E3E vodafone
?23415901686xxxx = EC0E465164E4364F vodafone
?23415901107xxxx = EC0E4651140CCDA9 vodafone

?23433420354xxxx = EC0E046E707B190D Orange
?23433400580xxxx = EC0E044E15544D53 Orange

?23430892800xxxx = EC0E16B987191841 T-Mobile

The ? denotes that there may be an additional digit before the 2 as the
decimal IMSI's start with 9. Also in the decimal ones each pair of
digits is swapped round, for example the imsi at the top of the list is
shown as 29 43 51 xxxxx etc but is actually 92 34 15 xxxx etc. The
initial 9 can be ignored and the other 15 digits are your IMSI.
I can't confirm that the first digit is a 9 in the hex encoding, so it
is shown as ? for now.

Any help would be very much appreciated and may even warrant a paypal
reward if the successful applicant can correctly identify the last 4
digits of each IMSI and show how they did it. I have these as a means
to check. :-P

I should also add that this is for legitimate business purposes not for
cloning SIM Cards (I'm not interested in the ki, ICCID or any other SIM
Card info). This is purely handset -related.

Ta!