When startup Nextbit announced plans for its smartphone, the Robin, the company planned to offer it only on GSM networks such as T-Mobile and AT&T. But with preorders topping expectations, the company opted to do a second version that would work with CDMA networks like Sprint and Verizon.

But after facing a slow carrier-testing process and other hurdles that would have meant further delays, the upstart phone maker is canceling its plans for the CDMA version. The company is refunding all Kickstarter orders for that model (as well as any accessories purchased) and giving those who backed it a coupon for 25 percent off of the shipping version, should they want it.

Nextbit had already delayed shipments of the CDMA model until April and said it would have had to delay things further had it kept going.

In an apology note to backers, CEO Tom Moss said the company underestimated the obstacles involved with getting a device approved for use on Verizon’s network.

“We were not sufficiently doubtful of what we were told given everything we already knew from our experience at previous companies,” Moss said. “We were too optimistic, too bullish, and as a result we have to deal with our biggest fear, disappointing you, our supporters. This is bad for you, and this is bad for us.”

Moss said both the time and the expense of doing a CDMA version were more than anticipated.

“What people at the carriers — in good faith, given our need for quick answers — thought would take ‘weeks’ has turned into ‘months,'” Moss said. “What they thought would cost ‘hundreds of thousands of dollars’ has turned into ‘millions.’ And we’re still not there.”

Nextbit has already had to make some big changes in its short life. The company, which raised $18 million in venture funding in 2014, began as a cloud service that allowed people to easily switch between different Android devices with all their data intact. Last year, though, it announced it was shifting gears and would instead use its cloud service in conjunction with a homegrown device in order to showcase more of its abilities.

The Robin’s signature feature, aside from its unique design, is the fact that the device can automatically back up apps and photos to the cloud as storage space becomes scarce, with apps being restored on an as-needed basis.