Accidently bough US-Region Guardian Signs D:

[Lunafloon]

I have a pretty urgent question, and I hope this is the right place to post it! :S
I bought my boyfriend Guardian Signs for Christmas and it's just arrived in the post from Amazon, however it appears I accidently bought an American copy despite shopping on the UK Amazon. My own fault I know, but it wasn't made extremely clear at the time and I remember having a rough day.

It's already the 12th and if I'm going to even try and get a refund I need to do it soon, so I need to know if there's any way that the giving him the US version is going to effect the game play, or will it work exactly as it should?

I remember on my Shadows Of Almia game I got a Manaphy, a Darkrai and a Riolu, and if there's anything similar in Guardian Signs I'm worried they won't transfer to a UK copy of the main Pokémon games. There's also worry that it MIGHT be region locked and can't be played on a UK DS though they rarely are...
Please help, I'm an idiot and Googling doesn't give me many results.

[Bolt the Cat]

IIRC, if you're playing on a DSi or 3DS model, all games are region locked, but if you have an older model of the DS, don't worry about it.

[Lunafloon]

IIRC, if you're playing on a DSi or 3DS model, all games are region locked, but if you have an older model of the DS, don't worry about it.

Well he's planning to buy a 3DS eventually, and I know (though I'm not supposed to) that my mother has bought me the same game from the same seller and I play on a 3DS XL.
Does that mean I definitely should try and refund and replace them for UK versions? :/

[Cometstarlight]

If you want to keep from being region locked out of your game, you may want to consider so

[Bolt the Cat]

Well he's planning to buy a 3DS eventually, and I know (though I'm not supposed to) that my mother has bought me the same game from the same seller and I play on a 3DS XL.
Does that mean I definitely should try and refund and replace them for UK versions? :/

If you don't have an original DS or a DS Lite, then yeah, you need to do so. Any other model of the DS or 3DS will be region locked, so he can't play it.