After months of teases and relatively few details, Verizon today confirmed both a launch date and pricing for its mobile 5G service. The U.S. carrier will offer “unlimited” service in Chicago and Minneapolis for between $85 and $105 per month, a premium of $10 over prior 4G/LTE prices, starting April 11. But there’s more to the story.

Though Verizon previously said its 5G Ultra Wideband Network will offer both 5G Home and mobile 5G services using the same towers and standards-compliant 5G hardware, today’s announcement suggests that’s not quite ready to happen yet. The carrier is instead starting mobile service solely in Chicago and Minneapolis, with plans to “rapidly expand the coverage area.” Verizon’s existing prestandards 5G Home hardware and limited networks in Houston, Indianapolis, Los Angeles, and Sacramento apparently won’t be ready to make the switch on April 11.

Also somewhat surprising: Verizon is launching the service not with Samsung’s Galaxy S10 5G phone, announced last month at Galaxy Unpacked, but with Motorola’s 5G Moto Mod backpack for the Moto Z3 smartphone. The carrier says it will begin preorders for the 5G Moto Mod attachment tomorrow with a special offer — customers will pay only $50, compared with the normal $350 retail price, as long as a Moto Z3 is active on the same Verizon account.

Putting aside the limited number of cities with Verizon 5G, it’s clear the company is interested in actively pushing the Moto Z3 and 5G Moto Mod to day one customers. People who order the 5G Moto Mod on March 14 will get a free dual USB-C travel charger; a free Moto Z3 phone is also being offered with a new line of service on that day only.

“At Motorola, we proudly deliver innovations, like the 5G Moto Mod and Moto Z3, that change how people connect with each other and use technology in daily life,” said Motorola VP Rudi Kalil. “We’re very excited that the transformative 5G Moto Mod developed at our HQ in Chicago will soon be used by our own community, in addition to Minneapolis, to bring our bright 5G future to life.”

There are still some question marks regarding what exactly users will be getting for their $85 to $105 monthly 5G service fees. Verizon says that its “5G service plan comes with unlimited data,” but it’s unclear whether that’s “unlimited 5G data” or something else — the carrier’s $85, $95, and $105 monthly “unlimited” plans all have limits on data speeds past certain usage levels.

Even the most expensive Above Unlimited plan offers 75GB of “premium unlimited 4G LTE data per month,” with 20GB of 4G mobile hotspot data, while the $85 Go Unlimited plan has no 4G data and “unlimited” 600Kbps tethering speeds. Moreover, the company is not offering any specific performance guarantees for 5G service with the 5G Moto Mod — just “ultra-fast speeds” and “ultra-low lag time.”

Verizon also unsurprisingly notes that its 5G devices will automatically switch to 4G when they’re outside 5G service areas. Within Chicago, only five specific areas are currently listed as offering 5G service: The Loop, Magnificent Mile, The Gold Coast, River North, and Old Town. In Minneapolis, the list is Downtown West, Downtown East, and Elliot Park. Verizon is promising “30+ cities coming soon,” with additional locations to be announced throughout 2019.

It’s not entirely clear how 5G service will work with Verizon’s unlimited plans in practice. On a positive note, a FAQ section says that “5G data usage with the Moto Mod is unlimited, with no data de-prioritization” and that the Moto Z3 will fall back to Verizon’s 4G network when outside of the 5G Ultra Wideband coverage area. Whether this means Go Unlimited customers will fall from 5G to 3G speeds — and what the 5G speeds will be like — remains to be seen.

As an incentive to sign up early, Verizon is offering three free months of 5G service to users of its Verizon Go Unlimited, Beyond Unlimited, and Above Unlimited plans. After three months — during which access to 5G will presumably be spotty, at best — the service will cost $10 over the normal price of each plan. In the FAQ section, Verizon says its 5G service will only be available to Unlimited smartphone plan customers.

Updated at 8:30 a.m. and 12:05 p.m. Pacific: A Verizon spokesperson confirmed to VentureBeat that users of the company’s unlimited plans will see two distinct levels of service: “unlimited 5G data” when connected to a 5G network, then whatever limits there are on the “unlimited” 4G data plan they’ve chosen.

In the case of the $85 Go Unlimited plan, that means the personal hotspot feature will drop from 5G speeds to 3G-like speeds of 600Kbps — that’s kilobits per second, not megabits per second — when the 5G Moto Mod connects to a 4G network, with unspecified non-tethered 4G speeds. For the $105 Above Unlimited plan, the user would get unlimited 5G data when connected to the 5G network, then 20GB of 4G hotspot data on Verizon’s 4G network, with 75GB of standard, non-tethered/hotspot 4G data before “data de-prioritization” kicks in.

In other words, Verizon’s $10 monthly 5G fee should deliver great additional value for users near 5G towers, but with the potential of a huge whipsaw in “4G” speeds, depending on how much and the way you’re using your device. That’s despite the 5G Moto Mod’s brand-new LTE Advanced modem hardware, which is capable of achieving incredible LTE speeds with new tower hardware.