WA5210G only offers WEP when set as bridge. it is a 11G product. WA7510N offers WEP and WPA when set as bridge. I think it will be very secured when the wireless security like WPA or WEP is set up....

Put the two adapters in the same room. And pair them. http://www.tp-link.com/en/article/?faqid=258 is the powerline light on?

normally，there is no way to change Message Center number (SMS) .this is set by the ISP

You can try check and configure the wireless security on the tplink adapter first: http://www.tp-link.com/en/article/?faqid=398

You tablet does not have wifi function? as far as I know, the network adapter is designed to be used in the computer. maybe you can contact the tp-link or the tablet for technical advice.

maybe you can also try to draw a simple topology about the devices and network connection.