No such thing exists for either appstore or cydia.
Only thing you can have on the ipad is imessages.
More info in a same type of thread here: https://forums.macrumors.com/threads/1425323/
edit: i see people on the thread posted above have mentioned WifiSMS. Remote Messages is a new development, but the same issues mentioned on that thread are still present.
if your iphone is jailbroken (which your sig suggests), you could use either the free WifiSMS or the new (but not free) Remote Messages. Both of them set up a sort-of (unsecure) server that allows you to access and send messages off your phone via a webbrowser for a device on the same wifi network, using the phone's IP address + a specific port number.
WifiSMS, which I've been using for a long time is great, but rarely updated by the dev. Crucially, it doesn't support sending or receiving texts via imessage. I haven't tried Remote Messages (and haven't seen any reviews of it yet), but its main selling point over WifiSMS appears to be imessage support.
Hope that helps, I'd be interested to see how you get along.
Yea neither of those are what I'm looking for. I'm looking more for a way to have my phone forward all messages to and from my ipad so I can use it to message as if I were on my phone, but they would probably at least need to be on the same network, or tethered.
For text with GV the OP wouldn't even need Talkatone. The GV app itself covers messaging. With GV just about any browser can be used to send/receive. I use it all the time at work.