Cannot change voicemail number

[syinner]

I am having trouble changing the voicemail number on my phone. I keep getting the error

"Voicemail number change unsuccessful. Please contact your carrier if this problem persists."

I need to change it from 901 to 111. Any ideas why it will not allow me to change it?

 

[speedycolzalez]

Absolutely no consolation but I get the same error. Mine's a vanilla Desire with an O2 sim.

ETA; seems to be a common problem if you Google it.

 

[syinner]

Same here, got a giffgaff sim, which is on the o2 network. Strange that I can't override the setting!