The East 737's still have ovens (fwd galley only), but they were "deactivated" by pulling the circuit breaker back when US stopped having hot meals on the routes the 737's flew.

It's my understanding that West 737's don't have ovens, but I haven't been on one so can't vouch for that being accurate. Assuming it is, however, my guess would be that the 737's will continue to have only "cold" meals for uniformity since eventually (some time next year) the fleets will begin to intermingle.

And, yes, the F/A only has to push the circuit breaker in to use the oven on the East 737. So it is likely that you'll occasionally see someone heating their own food while you're stuck with the cold entree.

Jim