You can send an ip packet to a service, which will in turn send an sms or place a phone call on your behalf. Such services provide varying degrees of anonymity.

You can send an ip packet to a service, which will in turn send an sms or place a phone call on your behalf. Such services provide varying degrees of anonymity. The cost of such services is irrelevant in the present discussion, as we are dicussing sending targeted malicious messages, not untargeted spam.