Japanese wordplay = 語呂合わせ = Goro awase

Japanese wordplay relies on the nuances of the Japanese language and Japanese script for humorous effect.

Japanese double entendres have a rich history in Japanese entertainment, because of the way that Japanese words can be read to have several different meanings and pronunciations (homographs). Also, several different spellings for any pronunciation and wildly differing meanings (homophones). Often replacing one spelling with another (synonyms) can give a new meaning to phrases.

Goroawase (語呂合わせ?) is an especially common form of Japanese wordplay whereby homophonous words are associated with a given series of letters, numbers or symbols, in order to associate a new meaning with that series. The new words can be used to express a superstition about certain letters or numbers. More commonly, however, goroawase is used as a mnemonic technique, especially in the memorization of numbers such as dates in history, scientific constants, and phone numbers.


Numeric substitution
Every digit has a set of possible phonetic values, due to the variety of valid Japanese (kun'yomi and on'yomi), and English-origin pronunciations for numbers in Japanese. Often readings are created by taking the standard reading and retaining only the first syllable (for example roku becomes ro). Goroawase substitutions are well known as mnemonics, notably in the selection of memorable telephone numbers for commercial services, and in the memorization of numbers such as years in the study of history.
Mnemonics are formed by selecting a fitting reading for a given number from the list below.

Number Japanese kunyomi readings Japanese onyomi readings Transliterations from English readings
0 maru, ma rei, re o, zero, ze
1 hitotsu, hito, hi ichi, i wan
2 futatsu, fu, futa ni tsū, tū
3 mitsu, mi san, sa surī
4 yon, yo, yotsu shi fō
5 itsutsu, itsu go, ko faibu, faivu
6 mutsu, mu roku, ro shikkusu
7 nana, nanatsu, na shichi sebun, sevun
8 yatsu, ya hachi, ha, ba eito
9 kokonotsu, ko kyu, ku nain
10 tō ju, ji ten

1492 (the year of discovery of America) can be memorized as: iyo! kuni ga mieta! (derived as follows: i (1) yo (4)! ku (9) ni (2) (ga mieta)!), meaning: "Wow! I can see land!" or i (1) yo (4)! ku (9) ni (2), It's good country.
23564 (23 hours, 56 minutes, 4 seconds, the length of a sidereal day) can be read "ni-san-go-ro-shi", which sounds very similar to "nii-san koroshi" (兄さん殺し), or in English killing one's brother.
3.14159265 (Pi) can be read "san-i-shi-i-ko-ku-ni-mu-ko"(産医師異国に向こう), meaning "An obstetrician goes to foreign country.".
4649 "yoroshiku" (derived as follows: "yo" (4) "ro" (6) "shi" (4) "ku" (9)) means: "Nice to meet you."
18782 can be read "i-ya-na-ya-tsu" (いやなやつ) – meaning unpleasant guy
37564 can be read "mi-na-go-ro-shi" (みなごろし), meaning massacre, or kill them all.
893 can be read "ya-ku-za" (やくざ) or Yakuza. It is traditionally a bad omen for a student to receive this candidate number for an examination.
573 stands for "ko-na-mi" or Konami. This number appears in many Konami telephone numbers and as a high score in Konami games.
765 stands for "na-mu-ko" or Namco. Derivatives of this number can be found in dozens of Namco produced video games.
.59 "ten go ku" is the title of a song from the Konami game beatmania IIDX. "Tengoku" (天国) means heaven.
3923 "san kyu ni san", or "Thank you Nissan!" (Nii-san means elder brother, so it is more like "Thank you, brother."). Found in the Online Comics of NBC TV Show Heroes, for which Nissan is a sponsor.
634 "mu sa shi", intentionally set the height of Tokyo Sky Tree sounds like Musashi Province or Miyamoto Musashi, easy to remember among Japanese.
801 "ya o i" or yaoi, homosexual themed manga typically aimed at women
39 can be read as "mi-ku", as in Hatsune Miku, or "san-kyu" (thank you).

Goroawase is used extensively in Mahou Shoujotai Arusu, where the main character introduces it as a method to more easily remember and cast spells. This game is used in episode 400 of the series Detective Conan.

Souce: Wikipedia

Another example thanks to my friend Kousaku Otake:

4649 (yoroshiku)
114 (iiyo)
 117 (iina)
184 (iyayo)
223 (fujisan)
194 (ikuyo)
0141(oishii)
634 (musashi)
893 (yakuza)
197 (ikuna)
33 (mimi)
1122 (ii fuu fu)
808 (yaoya)
026 (ofuro)
1126 (iifuro)
1192 (iikuni)
093 (okusan)
1105 (itoko)
373 (minasan)
5963 (gokurousan)
29 (niku)
0103 (otousan)
9494 (kuyokuyo
084 (o ha yo/o ha shi)
39 (san kyu)
‎373 0843 731 (mi na san,o ya su mi na sa i)