How can I increase the number of rings before the call goes to my voice mail?

[SuperFred]

There are 2 different ways to do so depending on the device you own.  On some HSPA/LTE devices you have to dial *61* your cell phone number + time value (1 ring = 5seconds) + #+ send.  On other HSPA/LTE devices You have to dial *004*+your number+time value (1 ring= 5 seconds) + # + send.  To deactivate it you either have to dial #61# + send or #004# + send.