On old 3G $15 plan can I use US roaming addon

[MM62]

I’m still on the old grandfathered $15 (bumped to $18 last Oct) plan.  I’m kicking myself because I was too slow to accept the upgraded $18 4G plan which would have gotten me 1GB in data.  Now if I switch I only get 500mb. 
So I’m trying to hold out and see if anything better gets offered hence I don’t want to upgrade to 4G right now. 
Which brings me to the US $30 text talk and data addon. I used this in Dec 2024 on this 3G plan without issues.  Has anything changed like do I need to have a 4G plan to use the US add on now or will it still work on my grandfathered plan?  I have a newer iPhone. 

[hTideGnow]

hi @MM62 

the 4G plans are just for speed, with 3G going away, all plans will soon be 4G plans because 3G is going away soon 

but 4G plans really have nothing to do with what plan choices you have.  Yes, the current $18 only has 500Mb.  if suggest you to change to that first if you can.  Then keep checking My Account and text for better plans Like, PM offered some $18 subscribers with better $19 and $20 plan just couple weeks ago