All these SIMs register and unregister your phone number of the moment with a free PBX, like the awesomely full-featured and robust Asterisk, so that your calls always reach you, and they'd spoof the outgoing number so that your calls would be returned to the correct number. This is similar to the way that a home NAT router shares a single IP address among many computers, keeping track of who gets packets for which session when with a little lookup table in its guts.
The best thing about this plan is that by buying giant blocks of prepaid airtime and service, you're hitting the carriers where it hurts, by using the services enjoyed by their best, most profitable customers. Every countermeasure they take against your service is an impediment to their bread-and-butter types. Those great customers form a human shield for your surgical strike on the carriers.
Maybe it won't work -- but what's the worst thing that could happen? You'd end up with a competitor to the telcos that de-fubared their business-practices, a geek carrier that treated us all like customers, not hostages.