Lost in the widespread hoopla over Google’s acquisition of mobile phone advertising firm AdMob was the company’s concurrent purchase of VoIP provider Gizmo5, which Search Engine Land’s Greg Sterling says will make Google Voice a stand-alone service.

Sterling writes that this could put the search giant into direct competition with VoIP market leader Skype, which boasts a worldwide user base of 480 million people. Search engine optimization (SEO) professionals must monitor Google’s move into the VoIP market closely, to ascertain what sort of SEO opportunities present themselves once Google Voice goes public.

Google already offers a Goog-411 service, effectively extending parts of its search functionality onto the mobile platform. This, coupled with the increasingly rapid adoption of Google’s Android cell phone OS, could give the company a solid bridgehead into the mobile market, creating new fields of opportunity for search engine optimization (SEO).

In another article about Google Voice, Sterling notes that consumer privacy advocates are troubled by the further expansion of Google’s data indexing, saying that the extent of the data collection raises questions about the security of personal information.