It is a possibility according to an interview with Pierre Perron, Sony Ericsson France General Manager:

“Mobifrance: Xperia X1 loads Windows Mobile. Are all models of this range will work with this operating system?

Pierre Perron: Not only, we work with all operating systems. We even share important in the UIQ platform. However, with Xperia, we send users “Experiencers.” This clientele demanding that wishes to all the technology and innovations in their mobile terminal without compromise. The range will be enriched Xperia
Other smartphones running Windows Mobile or Symbian or UIQ or other which will complement this range. “

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