The best way I've seen most pros do it who record their podcast in this manner is to use the Google Voice idea and leave messages for the hosts to retrieve and answer at their leisure. This would put a lot less stress on everyone involved. Listeners don't have to force themselves to stick to a specific time frame (and have no idea what has been said before hand in the podcast) and the creators can prescreen calls to their liking and pick the ones that fit their topics best.

The other option that is really simple and Britt has suggested it before but I don't think anyone has taken her up on the offer yet: Record an mp3 and email it to werenotdeadpodcast@gmail.com. Same exact principle and just as simple. You don't have to over think it. Just keep it simple