"phone carriers are accused of not doing enough against spam (or cold callers) too"
A mail server provider may not be responsible for spam unless it actively supports it and helps the spammers to avoid detection and blocking, once notified of the illegal activities.
There could be little difference between a legitimate bulk e-mail, and spam, without looking at the contents, sure.
The same is true for cold calling. If cold calls are regulated, and a telco knowingly helps spammers to break the law, they could and should become liable too.