* establishing of arbitrary phone calls

From RFC 3966 (http://www.faqs.org/rfcs/rfc3966.html):

11. Security Considerations

The security considerations parallel those for the mailto URL

[RFC2368].

Web clients and similar tools MUST NOT use the "tel" URI to place

telephone calls without the explicit consent of the user of that

client. Placing calls automatically without appropriate user

confirmation may incur a number of risks, such as those described

below:

o Calls may incur costs.

o The URI may be used to place malicious or annoying calls.

o A call will take the user's phone line off-hook, thus preventing

its use.

o A call may reveal the user's possibly unlisted phone number to the

remote host in the caller identification data and may allow the

attacker to correlate the user's phone number with other

information, such as an e-mail or IP address.

So, if you are referring to the callto: security risk on most all mobile browsers, they already know.

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