Hi Rod, sry long post follows...
This is the set up I would recommend: If you can get rid of your fixed line at home then do so... you may need it if you are on ADSL connection, I would not have one but for the family need (daughter and wife).
Get the iPhone from Telstra on the Next G network, check your usage and get what ever plan will cover it, the one I use is on a $99 dollar a month plan which gets you $1200 in calls and texts, Unlimited text messages to standard aussie number and 2.5GB of data (though I transferred from a business plan and for some reason I get 5gb a month). I can get lots of that back on tax
Get the iPad 3g but DO NOT get another plan for 3g access. You tether your iPhone to your iPad ('Personal hotspot' they call it now) and your iPhone data allowance is used for your iPad internet access... the iPhone becomes the iPads modem, I am actually on this set up now but on my Laptop PC, works on any bluetooth (or line) connection. You also need the 3G iPad as it has the built in GPS, the WiFi only one does not have the GPS inbuilt, requiring after market purchase.
Buy OzRunways... absolutely AWESOME app. Still could do with some development in Flight Planning and available Nav screens but it is 98% there already. get NAIPS App it does ... well... NAIPS! Get Dial-a-Wis app. I also have an App called 'Co-Pilot' I got this because it has a pretty good flight planning function with weather update to your flight plans, all ICAO field identifiers are in there (though being a US app I am not sure where the weather comes from, though it does generally reflect NAIPS, kinda sorta reflect NAIPS), it is not very intuitive to program but once you sort it out it is not so hard. It has a very simple and easy to see Compass/Nav screen which you really need on the iPhone.
Ozrunways is not real good on the iPhone because of screen size... not the programs problem... it is still usable just harder to see, but I used my iPhone (with those apps) ONLY as my GPS Nav and weather device from Tara to out near Cameron's Corner over a weeks flying...in a Drifter... only two problems I had: one when my iPhone was sitting in the sun for quite a while as I messed around getting ready for flight and it went into thermal shut down. As soon as I got airborne it cooled and fired right up again. Co-Pilot 'froze' once or twice, turned the App off and restarted... all good. Sending text messages while flying was available almost EVERY mile flown. Could listen to music with auto-mute activating when the radio fired up, make phone calls too though not worth it open cockpit:blah blah:. I am contemplating the iPad as well now. I have flown with them in other aircraft (and one of our crew used it in a Drifter on that trip) as they are really needed to get full functionality from OzRunways. I could have a 'glass cockpit' Drifter in the future
As for the Garmin comparison: buy a glare screen shield for the iPad and I never had any faults with GPS locks. You can't use your Garmin to surf the web and check your e-mails... while away (if you really WANT too). The weather on OzRunways has BOM radar...