I think that edbro wants to port his number from one provider to another, so not only change phones.
I have ported numbers in my country, which is in the EU. Porting a number means a new SIM card is needed. When the new SIM card is activated with the same number, the old SIM is deactivated. Will the new phone come with an already activated SIM card? Because here the SIM cards come separately and they are activated the first time when you use it.
Basically the EU way was (is) that phones were locked to a network, but a networks card could be used in any unlocked phone.
This does not apply to all telecom operators. There is one in my country that does not lock phones to its network, so a SIM card from another company can be used.