Additionally, if the numerical IP address is different (as much as possible of the 4 x max 3 digit blocks) this helps convince the search engines that the source and target URLs are not owned by the same person/organization.
One further value add to any link is where the words in the Title of the Source URL match in part that of the Target URL.
You can get all of the above for Free by just submitting http://abc123.teldial.com to the search engines, where abc123.tel is your domain (or subdomain) that contains a Phone (and optionally Email) link, so that http://abc123.teldial.com generates a valid page.
Once the search engines index http://abc123.teldial.com they will see a 1-way link to your domain http://abc123.tel
Try it for yourself - here's two examples http://mikeseaton.teldial.com and http://telnic.teldial.com - full details are at http://TelDial.tel
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