Charlie,
If SIP is blocked, then it is at the carrier level. Some phones have SIP clients, which use port 5060. Although
some carriers try to block SIP in general, just never use 5060 and you will usually be ok.
Bottom line: focus on the carrier side where you live to see if they block VoIP and don't worry about the phone.
73,
Mitch DJ0QN / K7DX