I am currently connected to Movistar in Mexico. To do so I went to settings -> Mobile data -> Network mode -> select GSM/UMTS only. Then Available GSM Networks -> Select automatically. It took a moment to register with Movistar, but once it did it automatically connects after airplane mode toggles or restarting the device. When in Brazil it was the same process to connect to Vivo.
I was able to enable from my account on the sprint site without calling. After checking my usage from the sprint site, IVR data and texts are accurately reflected without additional charges. In addition, wifi calling worked and was reflected in my usages accurately w/o additional charges.