It was on the first one I looked at.   

Onetel charge 29p/minute, NO connection charge.

Mike     A BETTER one for you to try for Cheap International calls could be CallnSave.biz
On their site, (don't worry about the Chinese for the moment!) the second drop box is the one for Uruguay.
This uses an 0871 number (BT=10p/minute, anytime)

0871 9900030

. Click on the link at the top to get translation & other information.
I know we're trying to get rid of them but this charge is all you pay, and it's at the rate your service provider charges.
Have a Google search for "0870 Uruguay" and you'll get a load more similar service providers.
Unless someone can find an even cheaper provider that is ?!  

Nice one Ken! We're really whipping down those rates for Mike to call Uruguay.
I had a good look at the other rates they do and there are some good ones there, especially to India and other South American countries.

Note

that there are minimum charges on some access numbers, and that prices change according to time of day, weekend, etc. Check the notes at the bottom of their rates list. 

Telediscount:

0844 5 661 661 (5p/min)

Thanks
Daniel

Or you can use

0870 794 5989 - Daytime 8p minute
0870 794 5989 - Evenings 4p minute
0844 570 5989 - Weekends 5p minute

Just dial the above numbers, then wait for the prompt and dial the country you want to call.  It works for loads of countries, mainly landlines, and some mobiles.

If you call 0871 570 8391, at 10p minute at all times, you can call even more countries, including many mobiles.

There is a recorded message on each of the numbers, which states which countries you can call on the access numbers.