According to a report on AllThingsD, we’re about to reach the limits of Verizon Wireless’s limited-time offer of unlimited data. The website reports that the wireless carrier plans to introduce tiered pricing next month for new smartphone customers—including those buying Apple’s iPhone 4.

If true, the report hardly comes as a surprise. Back in January, when Verizon became the second carrier in the U.S. to offer iPhone service, the company said it would offer subscribers a $30-a-month unlimited data plan for the iPhone’s launch, but stressed the offer was for a limited time. Verizon has been making noise for more than a year about introducing tiered pricing.

We’ve place a call to Verizon to confirm that current subscribers will get to keep their unlimited data plans—the company hadn’t responded as this article was posted—but such a move wouldn’t be without precedent. When AT&T introduced tiered pricing last year, existing customers could continue to pay for unlimited data. (The tradeoff, of course, is that AT&T customers who still subscribe to unlimited data can’t use features like tethering unless they agree to the carrier’s DataPro plan and its monthly data cap.)

(Update: In an email sent to Macworld Tuesday after this story was published, Verizon’s executive director of corporate communications Brenda Boyd Raney confirmed that “Verizon Wireless is making some minor changes to data plans including those for new smartphone customers. We will move to a more usage based pricing model in July.”)

AllThingsD says that Verizon isn’t providing specifics on the new plans, and in her email to Macworld, Raney said Verizon would offer more details “closer to the implementation date.” But AllThingsD cites a Droid Life report claiming that plans will range from $30 a month for 2GB of data to $80 a month for 10GB of data. Droid Life says the new prices will take effect on July 7.

By way of comparison, iPhone users who sign up with AT&T can opt to pay $15 a month for 200MB of data or $25 a month for 2GB; the 200MB charges an extra $15 for every 200MB of additional data, while additional data on the 2GB plan costs $10 per 1GB. Tethering via AT&T’s Personal Hotspot feature costs another $20 per month, but it gives users 4GB of data. (Under its current plan, Verizon also charges $20 for its version of Personal Hotspot, but its 2GB data pool is separate from the unlimited data subscribers get—that will most likely change next month when Verizon’s new data plans take effect.)

Updated on June 21 to include comments from Verizon.