Marketers have long had the chance to get their ads into Gmail with the expansion of the Google Display Network. Now, Google has announced that Gmail will roll out a feature that lets users call account holders' phones for free in the U.S. and Canada or at low rates in other countries, and this could translate into new ad opportunities.

The Gmail blog explains that voice and video chat users will be able to simply click a "call phone" button at the top of their chat lists, then they can dial a number or enter a contact's name to reach friends via phone. Users' Google Voice numbers will be displayed as the outbound caller, and users can also choose to receive calls made to them through Gmail.

This suggests consumers could be soon be spending a lot more time on Gmail, and ad-supported calls may be a good way for brands to grab gabbers' attentions. Perhaps Google will even offer advertisers click-to-call features, similar to Skype.

Skype unveiled Click & Call Advertising supported by Marchex earlier this summer, allowing marketers to pay just for inbound calls. When Skype users search the web for products or services, they have the option to click a "free call" button to connect to participating companies. The system lets marketers easily track the efficacy of Skype ads for lead generation, and they only pay for completed calls.

CNN Fortune reports that the Skype's ads are being warmly received by consumers because they are useful and relevant to queries. The source says there are 124 million international Skype users, which makes this feature appealing to marketers. Plus, CNN indicates many advertisers are waiting for the chance to run banner ads on Skype calls.

Marketers may also want to carefully follow the development of Gmail phone calls to see what opportunities arise. Google says millions of people use Gmail to chat with friends, so the platform may be a profitable new way for brands to connect with consumers.