In-App messaging. Desktop AND Mobil in one?

Hello all,

I’ve reached substantial completion on a Project Management application. ( And I’m NOT Technical ) What remains is In-app messaging and it is a must have feature! I’ve already tried Plugins such as ClickSend-SMS and TWILO but haven’t been able to get what I want out of them… ( Mostly due to my lack of technical ability? ) Our users will need to create/access messages both via the desktop application and mobile device.
This feature will get heavy use and I’m concerned it may drive down performance on an already leviathan sized build. How does one go about building this such that it can “come standard” on desktop version and be used separately as a mobile version? Thoughts?