To answer your question,
Common BCCH feature makes it possible to combine muti-frequency bands (eg. 900Mhz, 1800Mhz) into one cell having only one BCCH.
With this feature we can not only use a combined signalling, combined traffic channels with improved trunking gain but also can achieve tighter re-use of non bcch frequencies!
As far as I know most of the vendors have this feature.