I moved from Ireland to the US and kept my Irish number active - the cost was a €5 topup every 6 months.
Going in reverse is much harder - a lot of the budget phone providers in the US don't have any roaming offering. Best I can tell, you really need to have an account with a real provider, and that realistically looks like $20/mo (Google Fi), 20x more expensive than the reverse.
I moved from Ireland to the US and kept my Irish number active - the cost was a €5 topup every 6 months.
Going in reverse is much harder - a lot of the budget phone providers in the US don't have any roaming offering. Best I can tell, you really need to have an account with a real provider, and that realistically looks like $20/mo (Google Fi), 20x more expensive than the reverse.