In an attempt to compete with Verizon’s unlimited data usage plan, AT&T is now allowing subscribers that had an unlimited data plan in the past to switch back provided they had an iPhone before June, when the limited plan took effect.

As of this writing, the unlimited plan costs $30/month.  There are two limited plans, one that provides 200 megabytes of data for $15/mo, another that provides 2 gigabytes of data (usually more than enough for most people) for $25/mo depending on whether the person regularly uses streaming services like NetFlix or Pandora.