Sprint plan for watch, Verizon for Phone?

I bought a watch 5 a few months ago from sprint with a 1/2 price if you signed up for their $10 service for 2 years, effectively giving you the service for free. Sprint is going downhill in my area fast. Lots of drops, lag and no data service. After 25 years with Sprint I am considering moving at least some of my lines to verizon. Question - can I leave the watch on the sprint service which is tied to my cell number but port the cell number over to Verizon? This way I continue to have the deal for the watch.

I should add that I know I can pay off the watch for about $175 but the thing is I am only goign to port one line to Verizon to test it for a month. After the month I may move the rest over or jump back to Sprint.