By the look of it, you are very close. Try (untested code):
Dim objSysInfo, objUser
Set objSysInfo = CreateObject("ADSystemInfo")
Set objUser = GetObject("LDAP://" & objSysInfo.UserName)
set strtelno = objuser.telephonenumber ' Currently logged in User
Const HKEY_CURRENT_USER = &H80000001
strComputer = "."
Set objRegistry = GetObject("winmgmts:\\" & strComputer & "\root\default:StdRegProv")
strKeyPath = "SOFTWARE\shoreline teleworks\shoreware client\"
KeyPath = "SOFTWARE\shoreline teleworks\shoreware client"
strValueName = "AgentID"
strValue = strtelno ' <-- This sets the Telephone Number
objRegistry.CreateKey HKEY_CURRENT_USER, strKeyPath, strvaluename, strvalue