As I stated 1,5 months ago I've never had this problem again after finding which third party Apps were causing the issue. It's now nearly 5 months without problems.
I run a business too, so contacts are the most important thing, nut I never complained about my iphone, always being rock solid in every aspect.
We cannot complain Apple for third party App causing security issue in the sandboxing process, the Store is sooo big now and I think it's nearly impossible to check every single App in there for that particular problem.
Try another brand and you will end up finding more issues than benefits, in every aspect; we must think that we are using small computer, not cell phones and so we are responsible on what we are installing on them or, to be more specific, we must complain to the developer himself.
That said, try to format your iphone and install everything from scratch again, paying particular attention installing small groups at Apps per time, starting, of course, from the ones you really need.
Best regards