If you have the SE if probably is provisioned for Advanced Calling, where the 5c only used the 1x band of the network. I would go into Settings>Cellular>Cellular Data Options>Enable LTE (Select Data Only) and make sure Roaming is set to Voice & Data. Test this out and see how It works. May the force be with you.
Reliable service is definitely important so I understand your concern kbeaudoin2013. Lets get to the bottom of this.
Did the service issues start as soon as you activated the new phone? Is the issue only with calls? Have you disabled the Advance Calling settings and retested?
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