I had the exact same problem "connection error" all the time in specific areas, getting my simcard changed solved it for me, but now I have an other problem in the same areas (mainly at work) people tell me that my sound quality drops while on the phone. My provider (orange Austria) said that this can accour when talking over 3G. So I went on installing 2G/3G Switcher and it seems that by switching to 2G sloves the drop in quality, not realy the solution I hoped for but some workaround for those that can switch to 2G