Not flashed, cloned. IOW, you make it look like the donor phone (which would be another Verizon phone), software-wise, then you throw the donor phone away. Usually you'd use a cheap (as in found on Craig's list with a good IMEI, working, but something broken and not worth fixing, for about $10) phone as the donor, but you might not get all the S4 functions. If you use a Verizon S4 as the donor phone, unless you can find one in really poor condition but with a good (and readable) IMEI, it's going to cost you a new S4 - which will work but isn't really practical, since you might as well just use the new one.