I hope this doesn't turn into a rest/duty thread but.... If you are required/obligated to respond to that pager and/or are obligated to report to an assignment then you are NOT IN REST, and that is what can lead to a violation.
Sure, LR25, you can be on a pager/cell or on call 24/7 and that in itself is no violation (as long as you get the required 24 hour rest periods depending on what part you operate under). But if you were obligated to do so and report to an assignment immediately following then you and your company are violation of applicable FARs (135 Subpart F, 121 Subpart Q, 125.37, and possibly the catch all 91.13...)
And, as referenced above, technically there are instances where being "on the pager" or on call can in itself cause the violation, i.e. the required 24 hour REST periods required either per week or per quarter (135).
Every time this topic comes up whether here or out on the line, it sometimes comes across as a bunch of whiney weenie talk... "but the regs say this or that". But IMHO, if the vast majority of employers (that I have dealt with) didn't abuse these principles and exploit crews when allowed to, then we could use a lot of common sense, safety and airworthiness as the metric and would not have to rely on a lot of convoluted rules that half the POI's can't even seem to comprehend! Yeah right, sounds like one of those "Here in Perfect..." adds.