I've worked in a couple different environments in England.
Firstly, one where on I knew a bit of everything...So even though I was the DBA, I could get a call about citrix or a server down. I'd take a look and it if was beyond, you would just call the relevent person with more experience - It was a pretty horrible way to deal with support in my opinion. More times than not, I'd end up calling the citrix guys in the first few months.
Secondly, my previous job had 2 SQL Server DBA's and 2 Oracle DBA's. We just worked in a one week on, one week off format.
In terms of backups, the first role, everyone became the backup, although I was the only SQL Server backup as I was the only one with any real experience. The second role, we were expected to respond within 30 minutes. I was the backup if the support team could not contact the on call DBA and vice versa. It happened now and again for both of us but not too often so it wasn't really an issue.
As for pay, we had a flat day rate for Monday to Saturday and then double time on a Sunday and tripple time on a bank holiday and quadruple time when you was lumped with Christmas Day, Boxing Day and New Years Day! The policy was also that any call was chargable if it required you work for more than 30 minutes. We'd then get paid, based on our hourly salary. On top of that, we'd have patch windows (midnight to 2am or 5am to 7am) so that would be billable too.
It was ok and I made a good chunk of money working for this company but when you get maybe five or six calls through the night and weekends get taken up with calls it got too much for me and I left.
My current job is a kind of we call you, you work kind of role. There is no defined on call policy. I've been here 6 months and I've had maybe 4 calls. Of course, I get the odd weekend when doing an upgrade, but that's all planned.
I must admit, I prefer it now I am not on call. My basic salary is more, but overall I am on less without on the on call and my travelling costs are more but I'd not change it. When I lock my PC and head off, thats generally it for me ... I can go home and relax and play golf on a weekend without work calling me up and saying "we can see some database blocks....no, oh wait, they've gone, don't worry..." Not so bad on a weekend but at 4am...ggggrrrrrrrrrrrrrrrrr