I know of three ways, (1) Change the registry to allow sms notification to stop (2) Download Diamond tweak and change setting (3) download Advance configuration tool.
Instructions:
(1) Registry edit: Go to HKEY Local Machine\software\microsoft\inbox
Click on inbox, making sure Inbox is highlighted, select Edit, New Key
Name the New Key as "Settings"
Click on "Settings" (make sure the Settings is highlighted) and select Edit, New String Value
On "Value name:", key in SMSNoSentMsg and in "Value data", key in 1
Soft reset your device and test it with one SMS, and you will notice that the SMS Sent bubble is being disabled.
(2) Diamond Tweak (the easiest way), download and install this cab file and change the setting under SMS/MMS Messages 2.1 Sent notification change to disabled. (This tool also allows you to change the setting to keep your phone awake during calls)
http://forum.xda-developers.com/showthread.php?t=409540(3) Advanced Config Tool, works the same as diamond tweak but you can change other things also. For SMS notification on the Advanced Config interface scroll down to "messaging", open it up you'll see the both delivery and sent are disabled by default. With this utility you can change touchflo around and different things like that.
http://forum.xda-developers.com/showthread.php?t=418151