The following script, which is an adaptation of a script provided by a contributor to this site, worked under Mavericks. It doesn’t work properly under Yosemite (it hangs immediately if run directly, it hangs upon completion if run from the script editor. Any clues about why?

tell (current date)
set currentDate to its date string
set fileNameDateString to (its day as integer) & space & (its month as text) & space & year
end tell
set desktopFolder to path to desktop as text
set mobileFolder to (path to library folder from user domain as text) & “Mobile Documents:com~apple~Pages:Documents:”
– ~/Library/Mobile Documents/com~apple~Pages/Documents
tell application “Contacts”
###log (get its properties)
launch
activate
set theSelection to selection
if theSelection is {} or class of item 1 of theSelection is not person then return
set thisPerson to item 1 of theSelection
set companyName to organization of thisPerson – will be “missing value” if none
set personName to name of thisPerson
set lastName to (last name) of thisPerson
set firstName to (first name) of thisPerson
set nName to (nickname) of thisPerson
set salutName to firstName
if nName is not missing value then
set salutName to nName
end if

set nameVar to firstName & space & lastName
set theAddresses to addresses of thisPerson
if theAddresses is {} then return

if (count theAddresses) is 1 then
	set currentAddress to item 1 of theAddresses
else
	set addressList to {}
	repeat with i from 1 to count theAddresses
		set end of addressList to (i as text) & space & label of item i of theAddresses & space & street of item i of theAddresses
		--set addressList to addressList & space & street of item i of theAddresses
	end repeat
	
	
	set chosenItem to choose from list addressList with title "Write a nice letter to " & nameVar with prompt "Pick an address"
	if chosenItem is false then return
	set addressIndex to (word 1 of item 1 of chosenItem) as integer
	set currentAddress to item addressIndex of theAddresses
end if
set addressStreet to street of currentAddress
set addressCity to city of currentAddress & space & state of currentAddress & space & zip of currentAddress
set addressCountry to country of currentAddress

end tell

set buttonSmall to “Brief”
set buttonLarge to “Natter”
set thePrompt to “Are you going to be brief or natter on? (default is brief)”

display dialog thePrompt buttons {buttonSmall, buttonLarge} default button buttonSmall
set doWhat to button returned of result
set fileName to lastName & ", " & firstName & " " & fileNameDateString
tell (current date) to get day & space & (its month as string) & space & year
set letterDate to result as text
tell application “/Applications/Pages.app”

if doWhat is buttonSmall then
	set theTemplate to "TNC Small"
else if doWhat is buttonLarge then
	set theTemplate to "TNC Large"
end if

if theTemplate is false then error number -128
set currentDocument to ¬
	make new document with properties {document template:template theTemplate}
tell currentDocument
	###log (get its properties) # EDITED #######################
	tell body text
		
		set the first word of the first paragraph to letterDate
		if companyName is not missing value then
			set addressString to personName & linefeed & companyName & linefeed & addressStreet & linefeed & addressCity
		else
			set addressString to personName & linefeed & addressStreet & linefeed & addressCity
		end if
		if addressCountry is not missing value and addressCountry is not "United States of America" then
			set addressString to addressString & linefeed & addressCountry
		end if
		
		set the first word of the third paragraph to addressString
		set the first word of the second paragraph to linefeed & "Dear " & salutName & ":" & linefeed & linefeed & linefeed
		
		
		
	end tell
end tell

end tell

delay 0.1

activate application “Pages”
tell application “System Events” to tell process “Pages”
# awful trick to select something so that other commands do their job
keystroke “a” using {command down}
key code 126 using {command down}
repeat 4 times
key code 125
end repeat
–save currentDocument in file (desktopFolder & fileName) – save to desktop
–save currentDocument in file (mobileFolder & fileName) – save to mobile folder
–save currentDocument in fileName

end tell
set the clipboard to fileName