There’s a solution nobody has mentioned yet, which is using an iMessage bridge application (allowing you to message iPhone users over iMessage). If you have a machine running MacOS, I just started using one called OpenBubbles that works great and, unlike other bridges (AirMessage or BlueBubbles), doesn’t require you to spin up and run a Mac as a server.
Alternatively, iOS 18 drops this month and has support for RCS, as some have mentioned. This is assuming you use Google Messages…