iPhone 4S call forwarding keeps turning off

[Academy City]

Everytime I tried to call forward my mom's iphone to another number, after entering the new number and go back to the call forward screen, the on/off switch always greys out and switch back to off after a few seconds. Was wondering has anyone experience this issue or knows a solution to it. Many thanks.

 

[dictoresno]

thats usually a carrier option/service. does your carrier allow it?

 

[Academy City]

thats usually a carrier option/service. does your carrier allow it?

I doubt ours have it, I asked my dad to give us the cheapest smartphone plan.