...

Each SIM has a 'default' number, and if they want to instead use a

number they

...

pre-registred, have them text a 'token' (long enough not to guess a valid one, but not too long as to be annoying). That token is just displayed on eventphone.de when they register a number as 'GSM' without an IMSI.

ok, the other way around. The token is a unique value that they have

to SMS to

OpenBSC... great idea. I like it that way.

i would like to ask eventphone to add a 10 digits token to the registration tool. this way it is hard enough guess. the token shall be generated randomly when not yet assigned to a phone number. the token is used to authenticate:

- by sending SMS with the token (like said above) - by dialing a service number and entering the token - by giving the token to the GSM help desk.