I believe if your cell number is on file in your Leidos user profile as well as the tail number is listed as being you also, it'll still send you text messages no matter how you initially file.
But my profile was so broken for a couple of years that I couldn't even update it without error and it took them nearly two years with an open ticket number to fix it (after I asked them four times to just delete it and I would start over, they finally did -- because some software update they did was breaking referential integrity on their database just loading my profile).
So I haven't tested it lately.
Meanwhile -- can you tether data from your phone to your iPad on your cell carrier? That's the easy way to make all the goodies in ForeFlight or other apps that need data at the airport, work if you have a non-cellular iPad or no data service on it. Or most FBOs seem to have free wifi these days, but not all.
Charges and fees per your carrier, of course, may vary, for tethering and data use.