I've been working on an Android app for playing on OGS the last few weeks, and I think it is ready for a first alpha release. The accept stones part has not received much testing, so you may still need to be near a web browser for that part of the game, but I have made many correspondence moves with no problems.
Depending on the settings in the app, the first click and drag on the board will zoom making it possible to play 19x19 on a phone which was difficult for me in the phone's web browser.
Bugs are expected, so you may want to play a few games against the bot first before trying to make a move in your important tournament game that has been going on for 4 months
Download link and screenshots here: https://nathanj.github.io/ogsdroid/
If you encounter any problems please let me know.