48 percent of marketers think Amazon's Alexa has the greatest potential for voice-enabled marketing. Just under a third say Google's Assistant is best, and only 17 percent feel the same way about Apple's Siri.

And Microsoft's Cortana?

Just three percent.

But almost 40 percent of marketers are doing no voice-first marketing today. That is despite the fact that 86.2 million Amazon Alexas, Google Homes, and Apple HomePods were sold in 2018, according to Strategy Analytics. More than 60 million homes now have smart speakers, and global sales almost doubled in the Christmas quarter.

Location marketing company Uberall surveyed 300 small and medium-sized companies to learn what marketing tools companies are building with voice.

The upshot?

Marketers are finding it hard to build voice-first advertising and marketing tools. Only nine percent said their budget was significantly increasing, while 26 percent said it was slightly increasing. And 38 percent don't do anything with voice.

This should probably not be surprising.

Voice is not an easy medium for advertisers to crack into, despite the long heritage of radio commercials. Smart speakers are typically on-demand media, and when consumers ask for data or entertainment, they want it immediately, not after a ten second ad spot.

It's still early days, says Uberall:

"With voice technology still in its infancy, it's possible that SMBs are waiting until it matures -- either from a scale or technology point-of-view -- before making it a more prominent part of their marketing strategies," the company's CEO Frloian Huebner said in a statement. "There is also a learning curve among marketers on best practices and campaign development that is likely stalling investments."

The big challenge?

Getting a good picture of the ROI voice investments can generate.

53 percent of marketers said that better insight into ROI would increase their investment, while 47 percent said they needed more targeting and personalization options.

Most interesting, perhaps: 40% of marketers want to develop their own interactive voice channels, according to the study. That will require technologies like SoundHound, which allows brands to essentially create their own version of Alexa.

Interestingly, with Apple's recent acquisition of PullString, which could help Apple develop infrastructure to enable voice apps for its voice assistant, Siri could get more attractive to marketers over time.