It depends on your content. Earlier it was less than 150 links. But now you can have more links. Google tries their best to give better user experience to their users. So you should have enough stuff to help your users. You can support the stuff by adding links. If you are doing it correct , there is no limit for links.
Yes you can use unlimited internal links as per your content and services. You need to use high quality content for each internal links so that when any one visit at your website and internal link pages then find it a quality, informational and useful content which he is exactly finding.
From historical reasons, Google used to recommend less than 100 because the bots they sent couldn't process them (now it is different ofcourse - http://searchengineland.com/googles-matt-cutts-we-dropped-the-100-links-per-page-guideline-but-we-may-take-action-if-it-is-too-spammy-178197) If you are talking about creating internal links for ranking purpose, 3-5 links in the content body would be a good place to start. The key is to make the links relevant and not spammy.
Don't spam! Beyond that, I wouldn't worry too much about the number of internal links. Out of the total 340 pages on my website, by far the most popular in Google search is http://www.jimfeeney.org/morebibleteachings.html It has about 80 internal links and just a small amount of text. This page is the main index of my website's content. So it quite properly has lots of links. Google correctly understands that and does not consider it spammy.