Information regarding 400, 900, and 1800 MHz Band for GNU Ra

I was wondering if someone can give me valuable suggestion on the
frequency
bands of 400, 900, 1800 MHz. I was ordering for the USRP and other
hardware,
and was surprised to see that the daughterboards for these bands are
currently unavailable.

Are more people working in these bands so that the hardware was out of
stock
due to heavy ordering? and if yes, then what is the advantage of using
such
bands other than 2.4 GHz?

Thank you.

Tarun Mani Tiwari