But that would require you to trust them to actually delete it, if you don't trust them to not abuse your number that's kinda a non starter I would say.
In Europe at least, laws are very clear about "if I click the delete button, you have to delete it". All big companies stick pretty closely to those laws because the fines are huge.
There are also laws against using data for some other purpose than it was collected for, but they're less well enforced, and it's pretty frequent that a sneaky T&C clause let's them use data for something else.
Well from the article you have two examples from twitter and facebook that surely didn't care about laws.
And since they don't believe they will get caught (probably due to their track record with getting away with everything) there is no reason to care either.
And they don't have to be as blatantly stupid to send ads to the numbers, they could do as facebook, use it for a shadow profile.
You are being downvoted because nobody in their right mind would start the name of such a function by a capital. It would immediately get associated to the Windows API.
There are also laws against using data for some other purpose than it was collected for, but they're less well enforced, and it's pretty frequent that a sneaky T&C clause let's them use data for something else.