The Gemara establishes in the ninth chapter of Masechet Berachot (58B) that when one sees a dear friend whom he had not seen in a period of thirty days or longer, he must recite the Beracha of "She'hecheyanu," with "Shem U'malchut" (meaning, with the phrase, "Hashem Elokeinu Melech Ha'olam"). This applies specifically with regard to a dear and close friend, with whom one feels genuinely excited to reunite. This Halacha is codified in the Shulchan Aruch 225:1.
Interestingly, however, the Ben Ish Chai (Rabbi Yosef Chayim of Baghdad, 1833-1909) in Parashat Ekeb, Halacha 14, citing the Chesed La'alafim (work of Halacha by Rabbi Eliezer Papo, Bulgaria, 1785-1828), ruled that one should not recite She'hecheyanu in this situation. The Chesed La'alafim explained (listen to audio for precise citation) that given the unfortunate prevalence of false flattery, a person might recite She'hecheyanu upon being reunited with his fellow simply to earn his favor, without feeling genuine delight over seeing that individual. If somebody recites this Beracha when he does not experience sincere joy over being reunited with this individual, the Beracha is a Beracha Le'vatala (a purposeless Beracha). Therefore, the Chesed La'alafim ruled, nowadays we should refrain from reciting this Beracha upon being reunited with close friends.
Nevertheless, Chacham Ovadia Yosef writes in Halichot Olam, Helek 2, page 183, that in situations where one quite clearly experiences true joy, such as when a child and parent see each other after a period of thirty days, then he should, indeed, recite this Beracha. Since it is clear that a child and parent genuinely rejoice upon seeing one another after a long period of absence, there is no concern for insincerity, and one should therefore recite this Beracha. The same applies to a reunion of siblings or other relatives, or when one sees his close Rabbi after having been separated for thirty or more days. In all these cases, the feelings are very clearly sincere, and a Beracha is thus warranted.
Does this requirement apply if the friends (or relatives) had maintained contact during the interim period, such as through written correspondence or telephone conversations?
The Mishna Berura (commentary to the Shulchan Aruch by Rabbi Yisrael Meir Kagan, the "Chafetz Chayim," Lithuania, 1835-1933) in seif kattan 2, indicates that one would not recite She'hecheyanu upon being reunited with a friend if they had corresponded with one another in the interim. Many others, however, including Rabbi Moshe Halevi Z"L, in his work Birkat Hashem, as well as Chacham Ovadia Yosef, in his Halichot Olam (ibid), disagreed, and held that this Halacha depends on the friends' seeing one another, and not on correspondence. Therefore, even if the two had corresponded regularly or spoken regularly on the telephone, when they see each other in person for the first time in thirty or more days, they recite the Beracha of She'hecheyanu.
Summary: If a person sees a close friend of relative for the first time in thirty or more days, and he clearly experiences genuine joy as a result – such as in the case of children and parents, siblings, or a student and his Rabbi – he recites the Beracha of She'hecheyanu. This applies even if the two had maintained regular correspondence in writing or by telephone during the interim period.
