Generally speaking its a bad idea to outsource "critical infrastructure", and that seems doubly true for a software product. Imagine if the chinese government had an office set up in the Huawei office, and "conspired" to inject a backdoor into their base stations. There's the potential to completely commandeer our cellular network or worse to silently use it as a method to ease drop on conversations from government or business executives. According to news reports, these fears aren't as farfetched as they sound either.