In theory an all-in-one phone/ereader would be a very convenient combo. However, I would check out the battery life before getting it. How many hours of talk time? How many hours of reading time? Will the battery last all day?
I read for a long time on a pda-sized device and you will probably be happy with it. However, I doubt I would like it today. Although I've never used a Jetco, the comments I've seen here on MR tell me I would probably be happy with it. However, for my son I'm thinking about a 5inch eink device. The current best bet (soonest availability in the US) looks to me like the Astek EZReader. The manufacturer is predicting August availability. My guess is September.