[dheera]

At least now, Google only permits you to get a Voice number if you can prove you have another US number to forward to (they dial you to verify). Although I do have a US number, that's only because I happen to be working in the US right now; if I weren't I probably wouldn't.

Also a lot of apps in various other countries (notably China, because I'm familiar with it) do registrations via SMS, in which you need a +86 number in order to register, period. Smaller companies don't have the infrastructure to send international SMS verification numbers. Larger Chinese companies (e.g. Weibo, Wechat) permit registration with a US number, but they're larger companies who have servers in the US and infrastructure with US SMS gateways. So running around the world with a US number isn't always practical. If SMS is dethroned as a "de facto" communication method that everyone is expected to have, this might change. Other places besides China may also have a similar situation.