A lot depends on how much your employer is willing to pay you. In some countries there may be laws constraining this.
In the UK for instance, the EU working time directive applies and is applicable to on-call periods. However this addresses the amount of hours worked, also a lot of employers (unofficaly) require employees to sign waivers of their rights - AFAIK this practice, though seemingly widespread has not been tested in court. Also in the UK, there is a legally enforcable minimum wage - but you'd need to do some research on whether this is applicable to on-call periods.
Note even if you are not in the EU, then I would still recommend reading the document linked above - and using it in support of your position.
For more reputable employers, the common practice is that:
- on-call periods are voluntary
- a retainer is payable for the on-call period
- additional payments (usually at a higher than standard rate) are payable when a callout is triggered (sometimes there is a minimum threshold, then payable on the basis of the number of periods worked)
Certainly you need to be well-informed about the legal constraints, and I would recommend if you are negotiating for work and conditions for on-call support that you discuss travel-time and recovery periods.
C.