Using such an implant successfully would require a lot of training. When you make a phonecall with a mental command, it becomes hard to differentiate between thinking about calling someone and actually doing it.

Using uncommon pictures to control the actions of the implant might not be a good idea either. It is just too easy that mental stimuli from your environment trigger involuntary actions. Let's say your trigger for making a call to your boss is thinking of a pink elephant. See, you just thought about one and made an involuntary call.

A possible safeguard could be when the implant tells the user that they triggered an action and then monitors the mental reaction to the announcement before executing it. It should be easy to detect a stress reaction when announcing an action the user didn't actually want to do and then cancel it. The downside would be that it might make it difficult to get the implant to perform actions you want to perform even though they cause stress, like calling your boss to tell them you made a bad mistake or asking someone out to a first date.

And then during the telepathic conversation it might be hard for the implant to differentiate between those thoughts which are intended to be sent and those which are meant to be private. The conversation could become a lot more honest than intended. I will sell you this part for just 2000 credits. Heh, you idiot will sure fall for that. I am so glad you don't know that this piece of junk is not even worth 100. Wait, did I just think that or telethink that? Why do you want to strangle me?

However, we are perfectly mentally capable of making this differentiation when it comes to controlling our physical bodies. We can think about moving an arm without actually doing so. That's because we learned how to send signals from our brain to our limbs. This is a skill we were not born with. A baby is born with absolutely no motor control. It takes months until we learn even the most basic controls of our own body and years until we master it.

Getting a neural implant which adds new abilities to the body would be like getting a new bodypart. The user would have to learn how to utilize it, just like a toddler needs to learn how to utilize its arms and legs. Unfortunately an adult brain learns far more slowly than that of a toddler. It might be very difficult for most adults to learn how to use it. The situation is similar to that of people who lose their motor control due to brain damage. Some people are able to relearn how to use their limbs, but not all are successful and very few get close to the level of control they had before their accident.

On the other hand, when the implant is implanted during early childhood while the motoric abilities of the human develop, using it might become just as intuitive as any other bodypart.

Just like we currently have the generation of the "digital natives" who learned how to intuitively use the Internet during their childhood, your world might experience a generation of "neural natives" who intuitively learned how to control neural implants.