The first sign that HTC has reversed its downward spiral was the unconfirmed info that the HTC One had sold 5 million units (http://www.gsmarena.com/anonymous_htc_exec_claims_5_million_htc_one_phones-news-6082.php) not long after its end-of-March launch. Now we get something more official from HTC's monthly financial info, which shows a 48% increase in revenue for May compared to April.
(http://cdn.gsmarena.com/vv/newsimg/13/06/htc-may-financials/gsmarena_001.jpg)
The total revenue for May were $969.6 million, just 3.35% down compared to the same month last year. That's quite the reversal, considering HTC was seeing nearly 50% year on year decrease in revenue in the previous months.
The revenue for the January-May period is $3.06 billion, about $1.4 billion from Q1 (http://www.gsmarena.com/htc_posts_complete_q1_results_projections_for_q2-news-5958.php) and $1.6 billion for April and May. HTC should be able to hit its Q2 projection of $2.3 billion in revenue and even surpass it if the increase in sales holds up in June.
Source (http://www.theinfostride.com/file:///C:/Users/PETER/AppData/Local/Temp/HTC%20News%20Release%20HTC%20Releases%20Unaudited%20Revenue%20for%20May%202013.pdf) (PDF)
GSMArena.com