You could also just use the Calibre server itself to add books wirelessly (for free
) to a reader app like Aldiko (free version, android), Mantano (free version, android) or Moon Reader (android), MegaReader (iOS), Apabi (iOS) and Stanza (free, iOS) which although unsupported still works with iOS 6. The content server works within your home network.
I believe you can connect to the server outside your home network with Calibre Companion however I am unsure as I've never tried it.
How to for Calibre server + tablet here: