I assume this is an underground system. If it is on the surface, just take the hoses somewhere inside above freezing and let them thaw. For an underground sprinkler, the ground may not be frozen as deeply as the lines are buried so you may be able to drain them with little or no damage.

If you have ice in the lines, pour gas line de-icer (usually methyl alcohol) into the lines and let it work. We use that to open up the drain at work on a flat roof in the spring when the snow melts but the drain is frozen solid and a lake forms and water starts coming inside.......

Alternatively, pour full strength propylene glycol antifreeze into the lines where you unhooked them from the house.

Either way, after an hour, try to clear out whatever has melted and re-treat. You should be able to melt your way through the ice and it won't risk corrosion the way using salt will.

If you have any drains on the lines, make sure those are open to let any water drain out.

Thanks beeone, for sharing the information about frozen sprinkler system. It seems to be pretty helpful for us all.