When I had my first, I had a bath in the night when I was in labour (early stages) and I hated it, and when I reached the labour ward they offered me a pool birth, I said no way, but they convinced me to try it and oh was I glad I listened to them, it was the best, like the ton weight had been lifted... I was a completely different person... But also, if u get in and dont like it, u can just get out and have a land birth, as they call it... Only negatives are, if u end up needing a spinal of any sort, u have to get out, also if u need a drip then u cant have a water birth and also u cant use a TENS machine, for obvious reasons lol...
As for phoning before hand, all wards/hospitals are different, it depends on the amount they have and how many people are using them on the day. U normally phone before u go in anyway to pre warn them ur on ur way so just say to them when u call that u'd like a pool birth and they will tell u if they have one available, I would have thought....
Hope this helps
Siany1982