Cheap SIM card for mobile testing

I needed a generic SIM card solution for a mobile device test lab recently and searched for the best deal. Ultimately I decided on Three.co.uk Pay As You Go.

Unfortunately they limit their marketing and support to UK customers so US customers have to a do a bit more work:

1. Purchase a SIM card. They have lots of prepaid options but I chose their generic top-up SIM card option because it only cost a few bucks and can load minutes that never expire.
2. Insert the SIM card into an unlocked phone and then turn on phone.
3. Wait a few minutes and it will start roaming on the AT&T network and text you a temporary password.
4. Create an account by entering the phone number on the back of the SIM card holder (it will say "Your Three number" above it) and the temporary password from the previous step.
5. It will ask for an email but will only work with an email ending in ".uk" so grab a temporary UK email here and use that.
6. You'll get an activation link in your temporary email inbox. Click on it to login.
7. Click on the link for "My details" and then "Change email address". Enter your real email address and wait a few minutes to click the activation link that arrives in your real email address inbox.
8. Lastly, you'll need to add top-up minutes to your SIM card. Their default methods all assume a UK address so a simpler method is to use Ding. Select the amount you want to top up (make sure to scroll to the bottom to select a non-monthly non-expiring option), enter your phone number (keeping the default "+44" prefix), register for a Ding account with your SIM phone number, and then you can make a payment using either a credit card or PayPal. Once payment is made, Ding will display a numeric "PIN" code -- that's your Three.co.uk voucher code.
9. Login to Three.co.uk and click on "Top-up". Select "Top-up with your card or a voucher" and click next. Enter your PIN code from the previous step.
10. Enjoy!  Note: if the phone doesn't recognize the SIM or connect to the network, make sure roaming is enabled on the device and set the Network Mode to GSM.