Suggested text (probably needs work/re-write - wording?/jargon?/FAQsimplification?):
Adding of more voice post numbers
The list of voice post numbers at http://www.livejournal.com/phonepost/numbers.bml is a complete list of the numbers available. The voice post numbers are provided through a third-party VoIP (Voice over IP) provider. LiveJournal has no direct control over the distribution of numbers or area coverage; more numbers / coverage of new geographical areas are added as the provider extends into new areas.
LiveJournal users that do not have a voice post number available for the area code in their own city/region/country, may wish to use a calling-card or international calling plan, to reduce any cost they incur when calling a voice post number.
Users may also wish to monitor the lj_nifty community [http://www.livejournal.com/userinfo.bml?user=lj_nifty];
to keep abreast of any posts that users may make about different ways used to call voice post numbers.
Not sure about including a reference to lj_nifty userinfo/memories from an official FAQ, in this case. Stopped short of referencing any particular entries in the above text. :-/
Example support requests: