Can´t get network signal in portugal but in switzerland its ok

Hello. A friend of mine from portugal that works in switzerland has a phone that with a PT sim card from MEO, can´t get a network signal in Portugal, but in switzerland he says that it works ok. Can someone give me a pointer to what i need to do ? I have experience with android and roms but never messed around with an S5.
Do i need to flash a new radio or what ?
Thanks !

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