Disable voice control on iPhone 4s, ios7.1

My partner has a hand-me-down iPhone 4s, and a few months ago, the home button started playing up and not pressing. She started using the on-screen home button instead, which has solved the problem of not being able to press the home button.

Now though, the home button is more responsive, even too responsive. We started noticing that she had called random people (totally random, not most recent or near the beginning of the alphabet or anything) while the phone was in her bag, and occasionally while locking the phone, it would issue a camera shutter button as if it had taken a screenshot. Now it is frequently activating voice control, even if it is just sitting on the table.

It's pretty clear that the problem is that the home button is sticking down sometimes, and is often opening voice control, and as a result, dialling random people (apparently the voice dial software is oversensitive and thinks anything is a name, rather than saying 'sorry, cannot find "hrrghgsh" in your contacts'.

Other people who have had this issue have said that you can turn off voice dial (but not voice control) via settings > general > passcode lock, however my partner's phone has no such setting for voice dial in passcode lock, or anywhere else as far as I can tell.

Can anyone tell me where voice dial has moved, or if voice control itself can be entirely disabled (as one would expect to be possible) or alternatively, if the home button itself can be entirely disabled?

There is a way to make home button not to work wheb the home is lock. First activate Siri setting >General> Siri > ON Then If iphone 5s (may be it work in iphone 4a) setting >Id&passcode> there is an option where it tell to siri off when phone is lock. make sure you put it off. Thats it home button wont work when phone is lock. Preventing voice control to make stupid random call

I am experiencing the exact same situation on an iPhone 5. My home button is also sticking and the hyper-sensitive voice control is attempting to call people even when I am silent. As far as I can tell after painstakingly going through every single setting available, and researching on forums etc. The option of disabling voice dialling has been taken out of iOS7.1. I have not been able to find any mention of it anywhere.

EDIT: After reading through some information in Siri, I have restricted the use of Siri altogether (which may be a possible fix) You can do this at: Settings > General > Restrictions (Enter a passcode lock) and deselect the bar next to Siri as allowed content.

This setting seems to have been removed. Prior to 7.1 it was in:

Settings > General > Passcode > Voice Dial > OFF

Since 7.1 things have moved around a bit in settings, and the equivalent area would now be:

Settings > Passcode

...only the option is absent. Hopefully it will be returned, as my sticky home buttoned iPhone 4 is also occasionally dialling nonsense for me.

So, to summarise, there seems to be no way to turn it off for iOS 7.1 on a non jailbroken iPhone.