i have made wake up call system as softphone.
It is available for download at www.pbillx.org.
It is freeware, but not complete tested. So, if someone is interested, please feel free to download and install it. Make the settings to run it as extension to pbx. If there some problems with it or you have other suggestions, please mail this issues to me.
Please view my post in asterisk forum biz depend on pms billing system, too.