You could change carriers to another CDMA network, provided the new carrier will activate that phones ESN. If they do, they'd provide some codes you'd have to enter into the phone under the NAM menu. Once finished, the phone would be activated on the new CDMA carrier, but you'd be limited to voice calling.
However, you could switch to a CDMA carrier that also offers an 8910, and flash your 8910 with that carriers firmware for that model for full compataibility. To do that, you'd need the firmware file, the drivers for the phone, a data cable, and a program called CUPST, or at least the 8910 CcPst included within it.
It's considerably more complicated than switching a simcard between GSM phones, but it can be done.