I had an free of charge airave since they came out and really liked it. Sprint provided me with an "upgraded" airvana that is supposed to be better than the airave...as long as you reset it several times a day.
I notice that I start losing my signal at first and then I start getting error messages that my (and my family's) text messages fail to send. Dialing the *99 still tells me that I'm connected but can not send texts. So, unplug the airvana and plug it back in and things start working again.
Sprint says they can't "see" anything wrong with it.
David