create table #Rates
(
	Country varchar(3), 
	FromDate datetime,
	ToDate datetime,
	CostPerSec numeric(5,2)
)

create table #Records
(
	Country varchar(3),
	Date datetime,
	Duration int
)

insert #Rates
select 'USA', '2012-10-10 00:00:00.000', '2012-10-14 23:59:59.000', 0.01 union all
select 'USA', '2012-10-15 00:00:00.000', NULL, 0.02 union all
select 'UK', '2012-10-13 00:00:00.000', NULL, 0.02

insert #Records
select 'USA', '2012-10-14 10:00:00.000', 10 union all
select 'USA', '2012-10-15 20:00:00.000', 10 union all
select 'UK', '2012-10-13 20:00:00.000', 10


select * from #Rates
select * from #Records


drop table #Rates
drop table #Records

select r.Country, SUM(CostPerSec)
from #Rates r
join #Records rc on rc.Date >= r.FromDate and rc.Date <= isnull(r.ToDate, rc.Date) and r.Country = rc.Country
group by r.Country

declare @FromDate datetime = '20121013', @ToDate datetime = '20121015'

select r.Country, SUM(CostPerSec)
from #Rates r
join #Records rc on rc.Date >= @FromDate and rc.Date <= isnull(@ToDate, rc.Date) and r.Country = rc.Country
group by r.Country

DECLARE @FromDate datetime = '20121013', @ToDate datetime = '20121015'

SELECT rc.Country, SUM(r.CostPerSec*rc.Duration)
FROM #Rates r
JOIN #Records rc ON rc.Date >= r.FromDate 
            AND rc.Date <= isnull(r.ToDate, rc.Date) 
            AND r.Country = rc.Country
WHERE rc.Date >= @FromDate 
AND   rc.Date <=@ToDate
GROUP BY rc.Country