You may call anyone with whatever means you have. Then it was with word of mouth, then bells, then loudspeakers, then radio, then television, then mobile phones.
You are trying to equate the word 'call' and how it is not defined in the Quran with the word salat and how your namaz ritual is not defined as well!
Are you seriously still trying to tell us that all the details of the namaz ritual was left by Allah to our ancestors to give us the details? Five times a day, 24/7 and it is not important enough for Him to tell us how to do it properly.
Do you have any verses in the Quran showing the methodology I posted for namaz? Be careful with your response, you must type with your index finger, fully straightened, nail cut back to skin, cleaned three times!