You can also use Google Hangouts if you have Wifi present. Or you can use an app like Textnow on Wifi.
Also recently Textnow is offering free SIM cards and free cell phone and messaging use if you are in an area with Sprint cell coverage you can have totally free cellular. I haven’t looked lately but this became available about 6 months ago I think. Unfortunately for me there are no Sprint towers here - closest one is about 90 miles away so it didn’t work out very usable for me unless I travel to that area. It does cost an initial setup fee of $10 which covers them sending the SIM card and giving you a cellular number. If I recall you won’t be able to use a whole lot of mobile data without getting charged but for calls or SMS it should be totally free.