Straight Talk is a Prepaid Cell Phone Service from Walmart, from the same company that brought you Tracfone prepaid phones and minute cards.
Straight Talk has a UNLIMITED pricing plan that allows for data, text, and web for $45 per Month (as of this writing). Is it really unlimited, probably not, but you're used to this false advertising from your current phone company anyway. A soft cap of 2GB has been mentioned as a possible limit where you can expect text messages indicating to slow usage.
They do offer cheaper and more limited service options.
Their Bring Your Own Phone (BYOP) program (http://straighttalksim.com/) allows for a SIM card (Micro or Standard form factor) to be used in your existing phone for either T-mobile or AT&T service.
It's about $65 to get started with the unlimited, BYOP plan. $15 for the new SIM card and $45 for the first month of service. Once ordered, they offer 3 day shipping with FedEx for free. This BYOP is recommended for unlocked phones only. This may mean you'll need to contact a customer representative. However, in AT&T's case they offer an online portal to request an unlock: https://www.att.com/deviceunlock/client/en_US/. Note that you must have completed your service commitment to AT&T for this to work.
Note: that upon request completion it takes about 6-8 hours to receive a unlock status response from AT&T. This response indicates you should wait another 24 hours to complete the Unlock (unlock process involves a backup and restore iPhone through iTunes in our case - unlock should be complete after restore).
In our case, we chose to use our AT&T compatible phone (iPhone) and ordered the BYOP SIM. Once we received the new SIM, we went through the following steps:
Preparation:
Have your AT&T account number, phone number you want to transfer from AT&T, serial number (red card), and the service card number for the first 30 days of service to prepare to complete the online forms.
Step 1: Insert SIM card
Step 2: Activate SIM card (http://www.straighttalksim.com/activate.php or call 1-888-251-8164 and follow the prompts to talk to Customer Service)
Step 3: Select the option: "Activate my Straight Talk Service with a number from another company Activate my Straight Talk Service with a number from another company"
Step 4: Fill in serial number Straight Talk provided (red card with number provided)
Step 5: Enter your ZIP code where you will use your phone the most (Home)
Step 6: Enter serial number on the $45, 30 Service Days card (Scratch off on the back of the green card)
Step 7: Create an Account
Step 8: Enter in Account Number from AT&T
Step 9: Enter in password from AT&T Account (login password)
Step 10: Review Account Summary and Complete
Note that with the new SIM card in it read "No Service" for about two hours. This meant we had no phone service on either the old or the new SIM card. Once service came back, we confirmed our old phone number ported correctly by making test phone calls and texting. iMessage and Web require that the phone be unlocked, however, we used http://unlockit.co.nz/ to quickly get an APN profile installed for Straight Talk and get started with mobile Internet, iMessage again.
Service so far is exactly as we remember it with AT&T. Our 3G speeds are still around 1-3Mbps depending on where we are standing in the house.
We highly recommend this as an alternative to your T-mobile and AT&T contracts.
