Interesting. I think there is a problem with this phone and the three network as I don't have the same issue with exactly the same sim in a nexus 5. Anyway, Motorola support said it might be a fault so mine has gone for repair. Apparently it's repaired and been despatched back to me but no detail of what they have done yet. Half expecting them to have done nothing but if they've changed a part or updated some firmware then it'll be interesting to see if it makes any difference!