As the name suggests, the size is what sets the phones apart from most other Android-based phones. Both models have a 2.55-inch capacitive touchscreen display with a resolution of 240 x 320 pixels. The pro model adds a backlit QWERTY keyboard that slides out from beneath the display, making it bigger and heavier. It measures 90 x 52 x 17 millimeters and weighs 120 grams, compared to 83 x 50 x 16 millimeters and 88 grams for the the Xperia X10 mini.
Both phones run version 1.6 of Android. Sony Ericsson said it will be possible to upgrade them to newer versions of the software, but did not say when.
Other features include a 5-megapixel camera with an LED flash, a standard 3.5 millimeter stereo headphone jack, A-GPS (Assisted-GPS) and an FM radio. The phones can access the Internet using either HSPA (High-Speed Packet Access) or Wi-Fi.
Sony Ericsson has put just four application buttons on the small screen, one in each corner, to make them as easy to reach as possible.
Just like the Xperia X10, the two new phones also feature support for Timescape, which is Sony Ericsson's application for keeping track of text messages, missed calls, and Facebook and Twitter updates, the company said.
Since its an Android phone there are also a number of Google applications pre-installed, including Maps with Street View, Talk and Voice Search.
The Xperia X10 mini and Xperia X10 mini pro will start shipping in some markets outside the U.S. in the second quarter. Sony Ericsson also hopes to sell the phones in the U.S., but hasn't yet set a timetable.
The Xperia X10 mini will cost about €350 (US$475) before operator subsidies and the addition of a QWERTY keyboard to the pro version will add about €20, according to a Sony Ericsson spokesman.
Sony Ericsson will also launch a pro version of its Vivaz phone with a QWERTY keyboard. The company seems to have taken the criticism that it lacks smartphones with QWERTY keyboards to heart. The Symbian-based Vivaz pro will start shipping in the second quarter and cost between €450 and €500, a Sony Ericsson spokesman said.
Sony Ericsson hopes that the three new models, the Vivaz and the Xperia X10 -- which the company has dubbed the fab five -- will help turn around the company's fortunes. Sony's CEO Howard Stringer was in Barcelona to show his support for the mobile phone vendor.
Sony Ericsson's president Bert Nordberg also promised that the software quality on the new smartphones will be better than on previous models.