First we'll cover setting up the plan on your iPhone, then cover tips to help keep your data and minutes down to a reasonable amount. To start, you need an AT&T or unlocked iPhone.
Go to an AT&T store (or website) and sign up for the $25/250 minute prepaid plan (aka GoPhone). Tell them you already have your own phone. Don't tell them you have an iPhone, it confuses things.
AT&T will sell you a SIM card for $25. No worries — this is a $25 prepaid credit that we will use soon enough.
Punch out the SIM card.
If you have an iPhone 4 or newer you'll need to size down the SIM to a micro SIM. Some stores have a punch tool & will do this for you, or you can buy one for $5 online.
Alternatively, you can carve out a micro SIM with an X-acto knife using your current micro SIM as a template. Make sure all the contacts line up properly and don't cut the chip!
Now it's time insert the new SIM into your iPhone. Start by turning off your cellular data connection (under Settings > General > Network).
Nexr, grab a small paper clip and bend out the outer end 90 degrees.
Use the end of the paper clip to open the SIM tray on your iPhone.
Swap in the new SIM and insert the tray back in to the phone.
If all goes well you'll see the AT&T signal meter in the top left of your screen.
By default, iPhones are not configured to use the GoPhone data proxy. In the next few steps we will update the carrier settings so you can use an AT&T pre-paid data plan on iPhone.
Open Safafi and navigate to unlockit.co.nz/ — you'll see the screen above. Click "Continue".
On the next screen, choose "Custom APN".
On the last screen, "United States" should already be selected. Choose "AT&T" for the carrier then click "Create Profile".
Safari will exit and prompt you to install the custom APN settings. Click "Install" and your phone is all ready for a data plan!
Now we'll configure your GoPhone account with a data plan and add some credits for calling.
Log in using your assigned phone number (printed on the purchase receipt for the SIM) and the last 4 digits of the number as your password. (If this password doesn't work, just reset it online.)
Choose "Add Money/Features".
Add the 1GB option for $25. This is plenty of data for most usage patterns if you keep downloads and streaming to a minimum while you are on the go.
You'll be asked to enter a credit card to pay for the data plan. Your account balance should be at zero now.
Enable cellular data again and you're ready to start using your new plan! And look at that, you even have fancy "4G" (HSPA+) data…
Reset your Cellular Data counter so you can track your data usage (Settings > General > Usage > Cellular Usage). It'll be less than you think, but here are some tips that'll help keep things in check…
Keeping Calls & Data Costs Under Control
First, avoid keeping too much money in your account. AT&T can never take more money than you put in. This is a plus over post-paid where you can be surprised by a nasty bill if you exceed your limits.
Get a free Google Voice number at voice.google.com and use the app to make calls & send text messages. You can also use Talkatone to make free calls when you are on WiFi! Saves you text & call costs.
You can make free calls from your Google Voice number using Gmail too…
…or using a traditional telephone with an ObiTalk box!
You have 250 minutes free each month. If you go over, calls are 10c/minute. And, no taxes! You also have unlimited text messaging which is handy.
Streaming video, especially HD video like HBO Go, eats data fast. Watch those at home on WiFi and sync some TED talks or podcast episodes to watch while you're on the go.
Streaming music isn't so bad but works out to about 15c a song to stream. (Even on traditional plans it's hardly better at 7c/song). Sync playlists for the commute using iTunes or apps like Rdio.
Also, avoid downloading apps over your cellular connection. Update at home or when you have free WiFi.
And that's about it. Let me know in the comments how it works out for you!