Unlike most acquisitions in the Content Technology Marketplaces that we cover, this one actually seems like one in which there is not much overlap between two vendors' offerings. Antenna Software, a provider of mobile applications mainly for enterprises, acquired Volantis Systems, a company focused on delivering content to mobile browsers, concentrated more on the consumer Internet.
As a result, Antenna can now offer mobile apps as well as web apps and can serve different use cases. It also gets access to new markets: Antenna is primarily USA based company while Volantis is headquartered in UK and has offices in Europe and Asia.
Although the offerings are complimentary and might not require any major rationalization, the back-end infrastructure of two underlying platforms will still need to get integrated such that applications can use same resources (such as a content repository). An example of this could be a native mobile app created using Antenna's platform that employs Volantis' device database to fine tune display logic.
If you are a potential customer, the benefit is obviously that now you have one company that can cater to both native apps and web apps. On the other hand, it could be riskier as compared to betting on two different companies.
IBM licenses parts of Volantis technology for its own Mobile Portal offerings including the Mobile Accelerator which is targeted to customers of WebSphere Portal. Even though Volantis open sourced their Mobility Server a while back, not all parts of their offering are open sourced. So if you are considering IBM's mobile offerings, add this consideration to your checklist of items to be clarified. Make sure you understand their roadmap and resulting implications.
On a side note: having acquired Volantis and its well regarded technology for delivering web sites to mobile handsets, perhaps some day Antenna will actually start eating its own dog food. The screenshot shows how its site appears on a Nokia E71 smartphone.