The 1911 'A Manual of Poisonous Plants' says that the smell of the flowers is poisonous and that handling them can cause a skin irritation. Millspaugh, however, says that this is false but does say it has a 'nauseous taste'. It is not mentioned by Kew Gardens/St Thomas's nor is it listed in the 'International Poisonous Plants Checklist' published in 2008.

Wink and Van-Wyk, however, in 'Mind-altering and Poisonous Plants of the World', also 2008, say that 'substantial ingestion' of the fruits induces 'disturbance of GI tract and CNS'. They classify it as Class II 'moderately hazardous' but don't provide any detail as they do with other, better-known hazardous plants.

Overall, it sounds like one of those where you shouldn't sit down to a feast but you needn't get worried if someone has nibbled one or two.

A tea made from the seeds is used in the treatment of asthma and bronchitis and is applied externally to wounds[222]. The pods are sedative and are thought to have cardioactive properties[222]. Distilled water made from the pods, mixed with eyebright (Euphrasia officinalis) and rue (Ruta graveolens) is a valuable eye lotion in the treatment of trachoma and conjunctivitis[7].
Quoted from http://www.pfaf.org/user/Plant.aspx?LatinName=Catalpa%20bignonioides
So, I would guess that the beans are not edible as such.
I answered this a few weeks back.