Then you may find my MIT-licensed passcode view controller — as seen in the mappiness app and in the short screencast below — of use.

See Github for the code and (scant) documentation.

We’re now sending about one million notifications a month, and it’s working beautifully. The obvious alternative — using SMS messages — would be costing us tens of thousands of pounds a month.

If you’re using or contemplating using Push Notifications, you may find these four points of interest:

1. Urban Airship offer a well-though-out and reliable service. But if you’re using them just as an intermediary in telling the APNS to beep users X, Y and Z right now — not making use of their scheduling or broadcast features, for example — it might well not be worth it. You’ll cut out a layer of indirection, and save money if you get big enough for it to matter, by talking to Apple directly.
2. There’s a surprising dearth of viable-looking open-source options for interfacing with the APNS. (APNS uses a binary protocol over a secure connection, and doesn’t like this connection torn down and reopened too often, so you can’t easily interface with it directly from a web app or cron job). But there is pyapns, an XML-RPC-speaking APNS provider built on Python’s Twisted networking framework, with client libraries for Python and Ruby. I’ve found this straightforward and rock-solid.
3. The APNS feedback service sometimes reports device tokens as inactive for no obvious reason, so make sure you’re prepared to hear from and reactivate users you’ve previously inactivated. (mappiness got bitten by this early on: a few dozen people were unable to authenticate to our server because they’d been reported as inactive and we’d assumed they were never coming back, despite that fact they had the app installed and Push Notifications switched on).
4. The app delegate method application:didRegisterForRemoteNotificationsWithDeviceToken: seems occasionally to return phantom zero-length device tokens — so don’t let your app or server get flummoxed by these. (We suffered from this on mappiness too: the bad device token got added to the front of a queue for sending from the app to our server; the server wouldn’t accept it; and this blocked all further data getting sent back until we fixed the server to silently ignore the bad tokens).

So: free modem. No further commitment. And the opportunity to buy access a day at a time for £2, on a train journey, for example, or in an airport lounge, where the cheapest paid-for WiFi option is rarely less than £5, and often nearer £10. Handy.

Update. O2 is no longer doing the modem at half price, but the Quidco cashback has increased so that it still fully covers the modem and a £15 top-up.

The dongle

The dongle, a Huawei E160, is a fairly pretty white thing, and it supports my Mac. So far so good. Unfortunately, the software and instructions have crack-smoking hobos written all over them. Huawei “Mobile Connect” is ugly, crash-prone, writes logs to the console like there’s no tomorrow (literally thousands of messages per minute), and has never yet successfully connected me.

Luckily, you don’t need to use Mobile Connect: once the drivers are installed, you can connect using the menu item for the modem. Or rather, once the drivers are installed and you’ve taken the following counter-intuitive and undocumented step you can.

Making it work

When it installed, my dongle was configured as Vendor: Other, Model: Huawei Mobile Connect – 3G modem (this is under System Preferences > Network > HUAWEI mobile > Advanced…). This sounds good, but it doesn’t work: there’s nowhere to enter your APN.

Instead, after much fiddling, I found I had to switch Vendor to Generic and Model to GPRS (GSM/3G). Although confusingly less right, this does seem to do the trick.

I also ended up downloading new drivers from the Huawei site. (Not for the E160. That would be too simple. The ‘Mac’ drivers for the E160 turn out to be a Windows .exe file. The drivers I’m using are supposedly for the E220). I’m not sure if this step was necessary or even well-advised, but it might be worth trying if you’re not having any luck.

Listen up, O2

Which brings us to the suggestion to O2. O2: I have an iPhone. It’s on your network. It supports tethering. I’m not about to pay you an extra £15 a month for the once or twice a month I want to use it. Let me use it for pay-as-you-go mobile broadband!

In this case you’d have saved yourself the full cost of a modem dongle — and generally, you’d be saving yourself the support costs and return costs associated with everyone who can’t get the horrible thing working. You’d have saved the world the cost of the resources and pollution required in manufacturing it. And you’d have saved me the pain of several hours fiddling with System Preferences, the inconvenience of another gadget to pack for every trip, and probable future kernel panics associated with Huawei’s flaky drivers.