Depicus Wake On Lan allows you to remotely wake a computer or other device that comply with the Wake On Lan protocol either on a local network or over the internet.
Full information about Wake On Lan can be found at http://www.depicus.com/wake-on-lan/welcome.aspx
NB: Wake On Lan and Wake On Wan will not work to wake up a computer using only wifi although you can use this application to wake up machines if you are connected to wifi or 3g. Also note that some Mobile Operators block UDP over their networks, try using a higher port number e.g. 4343