get one of these with a mobile plan

You don't have an account with 2talk by any chance?

I faced the same dilemma when my mum went into a retirement home. I ported her number to my 2talk account and got her a wireless IP phone. The rest home let me connect it to their wifi so mum ends up with a landline with heaps of free local & national calling for about $5 per month. I buy 100 mobile minutes a month so there is enough for her to make a few calls to cellphones if she needs to.

OK guys thanks for all the info - looks like the Vodafone Home Phone Wireless is the go.

HotDogBreath: Is the following worth a look at?
Mobile phone on low plan (dirt cheap ones for that amount of low calling) tethered to a landline via Bluetooth?
I played around with this idea a few years ago with a Uniden handset/base station. Worked fine for calls.
Benefits:
• she would have the benefit of using a ‘normal’ handset.
• Dirt cheap monthly running charges.
Downside:
• Mobile would have to be permanently hooked to power (and hidden away?)
• Change her number from landline suffix to mobile.

Had a quick look on Trademe and there are desk phones that can take a sim card. This should be more reliable?

Add a landline-on-mobile feature for $20/month and other people calling you would be none the wiser.