Just yesterday, Verizon announced changes to its prepaid plans to make them more competitive with rival offerings. Effective immediately, prepaid plans from Verizon now start at $30 and top out at $65 instead of $75. The notable changes affect the carrier’s two top-end plans. A $45 unlimited talk and text plan with 8GB of data each month replaced the old $50 plan that included 7GB of data. Verizon’s prepaid plan with unlimited talk, text, and LTE data then dropped to $65 from $75. Additional lines can be added to each plan with discounts ranging from $10 to $20 per line.

The new prepaid lineup is clearly an improvement for people who want service on what is still considered by many to be the best wireless network in the United States. As is typically the case though, the best comes at a price. People who use prepaid plans as opposed to postpaid often want the least expensive option. On Wednesday, T-Mobile launched a limited-time offer that undercuts Verizon’s newly discounted prepaid unlimited plan by a sizeable margin.

It’s not clear exactly how long T-Mobile’s new “limited-time” offer will be available, but there is one thing that is clear: it’s a much better value on paper than Verizon’s rival plan. For $50 each month, T-Mobile will give users unlimited talk, text, and LTE data. That makes it $15 less expensive than Verizon’s plan each month, which adds up to a substantial $180 annually.

While both the new Verizon plan and the limited-time T-Mobile offer include unlimited data, texting, and domestic voice calling, each one has a big benefit over the other. On Verizon’s side of the fence, subscribers get unlimited calling to Canada and Mexico in addition to the US. That’s a huge deal for customers with friends and family in another North American country. But with the T-Mobile plan, subscribers get unlimited tethering at 3G data speeds. Verizon’s unlimited prepaid plan doesn’t include any tethering.

T-Mobile’s special limited-time prepaid plan includes the same caveats as other similar plans in the Uncarrier’s portfolio. Subscribers who use more than 50GB of data during a single billing period will have their data speeds throttled “during congestion,” whatever that means (yes, we know what it means, but no carrier has a clearly defined threshold for what constitutes congestion). T-Mobile’s prepaid unlimited offer also throttles video streaming quality. The carrier says “video typically streams at 480p,” offering no further clarification on its prepaid page.

More information is available on T-Mobile’s website.