[mschuster91]

Yes, security and flexibility.

1) Security: telco laws these days often require registration of accounts to your personal ID (i.e. no anonymous usage any more). How would a pure soft-SIM be able to fetch the data from the network?

2) Flexibility: SIM is pretty much standardized. This means a newcomer MVNO just has to issue SIM cards and the customer can use any kind of phone (or other interface, like a modem, a 2G/3G shield, ...) to use the network. And if a device breaks, then the SIM card usually stays intact and can be placed in a new device. Not sure how to securely do this with a soft-SIM.

[potatosoup]

Wouldn't e.g. a username and password accomplish the same thing as what you're describing?

[vidarh]

Now any hacker that finds a flaw in a mobile OS will be able to impersonate you with another phone. For what gain?