Inter-symbol interference in ZigBee systems

In case of using equalizers with ZigBee systems, what type of fading does the channel show, flat or frequency selective, fast or slow?

Is the inter-symbol interference (ISI) problem encountered in ZigBee systems?

I am asking this question because I konw that ZigBee Systems transmit data at low rate (250 kb/sec), and ISI problem and hence frequency selective fading appear with high data rate applications. I found some papers employing equalizers with ZigBee under Rayleigh fading conditions, but the type of fading was not indicated.