Best answer by Daniel Gunn
When you go on a seasonal hold on your account you will not be able to get the old plan you had, you'd have to change to a current plan available at that time. The seasonal hold is only good for 6 months. As far as checking which phone has the seasonal hold or the current plan you have, all you'd need to check is on your self serve account and it will show which plan your line has on it at that time under the Plans and Add-ons tab.
Hope that helps answer your question