It reminds my good days programming simcards, i was the founded of a startup in Brazil that made a good use of simcard programming to store two numbers in the same simcard, around 2010 it's a cool and profitable, the thing is that i managed to insert a local imsi and an a north american imsi registered in the same card so everyone that travel abroad could be free of expensive roaming charges, them we sold the company and now days they are a reseller for some major carrier in US =)
I travel a lot and use a hacked up Chinese phone since it supports dual SIM pretty well but I'd rather use an iPhone. Unfortunately I want both my US and UK numbers and contacts slightly more.
It's not impossible, large carriers are still using DES to sign the OTA updates. Using rainbow tables you can crack the key and install an app which can break out of the sandbox and read the ki and IMSI.
