You will just need to insert the Curve's SIM card into your husband's phone and voila! The only problem, is that the card is another side so you would need to have a cuter to do that. Or you could buy a new prepaid SIM card for your husband's phone
Well the 5C uses a nano Sim. I'm assuming that your husband has a Sim card equipped curve and not a CDMA one? Either get it stamped to a nano Sim if it isn't multi cut to be able to snap to the size of one or just get a new Sim card and switch on self-serve and pop it in.