Well, for starters, the SIM card in the eCall system is only needed to receive a callback from the 112 service if the call drops, which the system automatically picks up. You can actually dial 112 without a SIM card in your phone, as a GSM device without one can still connect to nearby radio towers in a "limited-service set," better known as "emergency calls only."
I know some carriers have strange quirks in their SIM provisioning systems. For instance, it may take more than a few minutes or require a specific type of coverage (like UMTS) for an otherwise "dormant" SIM card to activate from limited service on short notice.