I was visiting NYC for a few days; had my unlocked iPhone 4s powered by an AT&T paygo sim, when the phone up and died. No signs of life. All attempts at resuscitation proved fruitless. BTW, I think the AT&T paygo with $25 data add on is definitely the way to use your (unlocked) iPhone in the US.

Fortunately I was staying within a few blocks of the 5th Ave Apple store, so I make an appointment at the Genius bar. The recent renovation seems to have streamlined the entrance to the store from what I remember years ago. After taking the phone in the back to examine, and being unable to determine the issue, the Genius just handed over a replacement. It was suggested I activate with my Rogers sim, which I had with me, instead of the AT&T.

After activation, I swapped out the sim but got the message of an invalid sim. Despite rebooting, etc, no happiness. By this time I had rejoined my wife and not wanting to put the day on hold and return to the store, Grand Central Station happened to be on the day's agenda. Bingo, I would get to see the new Apple store and more attention for my phone.

The Grand Central store is absolutely amazing as far as an environment. Super high ceiling and grand marble floors and walls. Unlike other stores I've been to, it's totally broken up and spread around the mezzanine, on both sides of a central staircase. Imagine a number of open rooms, linked by passage ways, with some nooks. Amazing space.

Met up with a Genius, who performed a DFU restore and was still unable to get the phone to work with either of 2 sim cards she swapped. Another replacement phone was provided. This time, the Genius activated the phone with her own sim and after a little further investigation, determined my AT&T sim was not working. How it may have messed up the 1st replacement phone was a mystery.

A couple of unplanned Apple store visits but a happy ending.

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Question for you: I assume you went to Unlockit - APN Changer for your iPhone (http://www.unlockit.co.nz/unlockit/) to get the AT&T settings for your phone? What do you do when you get back to return it to Rogers? Will a clear network settings work?

RoamMobility is another option for us Canadians, buy a 4G hotspot for $129.95 and buy 500MB to 5GB of data for $29.95 to $99.95. They also have combined talk+text+data plans for those with unlocked iPhones, which includes unlimited talk and text within the US AND Canada and a certain amount of data, starts from $7.95 for one day and 100MB, a week is $39.95 and comes with 500MB, they have a $18.95 three day/200MB plan, etc.

Since my phone is not unlocked, I'd probably stick with the hotspot and call back to Canada using Dell Voice or Skype. :)

The Grand Central store is NOT a typical open space store; it's spread around a number of rooms and nooks on an upper mezzanine overlooking the main station floor. Separate areas house the Genius bars, training areas, etc.

Yes, I used the APN changer. Once installed, it shows up as an App. Back in Canada, I just popped in the Rogers sim, go to the APN App and hit the Uninstall button and it's gone.

I looked into the Roam Mobility; on the surface it looks good but the problem is it is set up through T Mobile. In the US, T Mobile and iPhones don't play well; you only have 2G service, which is slower than dial up at times. My wife has an old iPhone which I put a T Mobile sim into for NYC and the data was almost useless. FYI the T Mobile paygo with unlimited talk & txt and 2G data is only $2/day, so why pay Roam Mobility rates? The 4G service they promote does not work with iPhones through their sim card; maybe the portable Hotspot would do the trick but that's an extra $130 and gadget.

Jeez. I just ran through 250MB in a day and a half, with limited use (for me). Looks like it'll cost me at least $50 for a week's access.

Too bad I deleted the "APN app" - but it's just a bookmark anyway. No biggie, I'm sure it just deletes the APN anyway, which you can do manually. Thanks though.