AIM on Smartphone estimated data usage? $24.99 Plan enough?

Hello, my friend plans on getting the HTC 720 (libra/UTStarcom 5800) when it comes out and was wondering if the $24.99 data plan (10MB) would be enough for strictly AIM on IM+ usage. Let's say she's on AIM all day (24/7) and sends an estimated 10000 IMs a month (that's combined in and out). $45 a month just to use AIM would be =(. On a side note, she doesn't want the ENV or any other phone. =)

Also, just to make sure, there is no way to get the unlimited VCAST for this phone for $15 because it is a smart phone right? I'm asking because the FAQ says no I think but, you can order the Verizon PN-820 Smartphone with Vcast as an option on Amazon.com so I'm a bit confused.

Last question is, can a family plan add the data feature on just 1 line? The verizon website doesn't seem to have this option.