I was a member of the Inetrnational Telecoms Union group that came up with a standard to allow users not operators to dial international codes and as ahs been pointed out while the country code, 44 UK 33 France etc is always going to be the same the way the domestic network worked all sorts of numbers were used to access 'international' .
At the same time this group was standardising the telephone push button pad as far as that was possible. In some countries the three letter groups under the numbers are slightly different . The key pad had two extra buttons * and # and although not used for setting up calls by users they were sued by international operators. Also some countries used ** to generate the + . When mobiles came along the EU and the GSM mobile phone governing body agreed that in Europe 00 would be the international access code but that didnt work anywhere so it was back to the plus sign meaning put your countries international access code here. it also signified it was an international number as not every country uses zero as an access code , USA for instance . trying to get a roomful of people to agree what to call ~ was a real herding cats effort
It was also supposed to be a recommendation that people would use + on business cards and letter heads but it also caused a lot of confusion. compounded by people giving their number as 44 0 7xxx xxxx
99 percent of countries need you to drop the ) but as always there are exceptions
standardisation , well the aviation business knows all about that with height in feet, runways in meters, wrights in Kg etc , nice idea to have a common set-hard to do
Soon