Xperia Pro/Neo/V/L :: It Loses Connection Regularly (re-opened)?

I have a Sony Xperia kyno V/neo V (MT11i), French retail version w/o branding - updated to ICS 4.0.4 via official Sony softwareMy provider used to be Free (France) which runs its own network but allows users to roam on the Orange France network wherever Free's newish network still lacks coverageMy phone seemingly randomly loses connectivity to voice and/or data service for also seemingly random periods of time - sometimes I cannot place or receive calls, sometimes I have no data connection while voice seems to work just fine, and sometimes there's nothing...Loss of signal often occurs while the phone is stationary in an area with normally fine network coverageI could not replicate the problem on a Nokia running Symbian and a Samsung running Windows Phone 7.5, but neither features a logging function of network signal like Android does The behavior of the phone seems highly unusual to me and while having no data connection for a few minutes is a minor nuisance, being unavailable for calls for minutes or even hours is simply unacceptable. I took a number of steps to solve the problem:I switched signal to WCDMA only (from WCDMA where available and otherwise GSM)I did a factory reset of the phoneI switched to another provider without domestic roaming (B&You, Bouygues)
Nothing helped.