“Data Plans from This Network Provider Cannot Be Added” error
This error likely means your phone is locked by the original carrier of purchase or a CDMA device.
This article explains more about a locked device. In summary, you need to find out if your device is carrier-locked and its network type at purchase. Here are a few places to check your devices IMEI:
Dial *#06# to retrieve your device’s 15-digit IMEI number, in case checking on your IMEI lock status.
CDMA Vs. GSM Phone
Some carriers like Verizon and US Cellular use the CDMA network, and phones purchased from them or for their network may not work on the GSM networks in use by much of the world.
Some phones may be blacklisted for reasons, and will not work. Try checking your IMEI.
Data Plans from This Network Provider Cannot Be Added
Your device can only use data plans from a different network provider.