Does Jailbreak unlocks iPhone 4 to international SIM Cards?

I have a iPhone 4 16Gb with IOS 6.1.3 locked to Orange UK, and i need to know if i can unlock it using jailbreak to use it in another band in Portugal (Vodafone). Is this possible?

I also know that IOS 6.1.3 its not currently jailbroken, but maybe i can Downgrade to 6.1.2 and then jailbreak?

Thanks.