Although it is not yet passed, the proposal will be presented next month to the European Council for passage "as early as possible." As the Commission itself wrote: "Key changes for citizens will include the end of mobile roaming premiums and a guarantee of "net neutrality.""
The benefits to EU citizens is obvious. For non-Europeans, it means they will be able to buy a SIM card in any EU country and use it in any other EU countries without having to pay roaming charges. Companies offering the cards can decide for themselves how much they will charge for them (to buy) and will probably offer different packages. Presumably, since SIM card could be bought anywhere in the EU, the competition should keep general prices reasonable.
The EU announcement