Can I use a 4g sim card for a 3g phone

[Rshim37]

I just bought a Samsung Galaxy Mega, I have a 4g sim from old phone but this new phone is 3g, can I use my 4g sim for a 3g phone?

 

[Titillating]

Shouldn't be an issue. You'd just get stuck on 3G. Might want to call your service provider just to confirm though.