A hardware phone keypad has 12 standard keys that also have emoji representation: 0️⃣ 1️⃣ 2️⃣ 3️⃣ 4️⃣ 5️⃣ 6️⃣ 7️⃣ 8️⃣ 9️⃣ #️⃣ *️⃣ . They are special in that they are actually using the standard Basic Latin digits and punctuation marks, followed by an (optional) variation selector and a (mandatory) combining character, U+20E3 Combining Enclosing Keycap. Many other emojis are represented in the same button style, depending on the vendor, e.g. media playback and navigation controls: ▶️ ⏸ ⏯ ⏹ ⏺ ⏏️ ⏭ ⏮ ⏩ ⏪ ⏫ ⏬ ◀️ 🔼 🔽 🔀 🔁 🔂 🔄. It should be possible for authors to request this style for all symbols that regularly appear on key tops, simply by using U+20E3: ▶⃣ ⏸⃣ ⏯⃣ ⏹⃣ ⏺⃣ ⏏⃣ ⏭⃣ ⏮⃣ ⏩⃣ ⏪⃣ ⏫⃣ ⏬⃣ ◀⃣ 🔼⃣ 🔽⃣ 🔀⃣ 🔁⃣ 🔂⃣ 🔄⃣.
The basic calculator keys are already available as emojis, ➕ ➖ ➗ ✖, and thus could use the combining keycap without any changes necessary: ➕⃣ ➖⃣ ➗⃣ ✖⃣. (Actual support for that is lacking, of course, and the results are awful.) Other operators would probably need VS-16, which are not yet in emoji-variation-sequences.txt, or U+20E3 would need to become an emoji.
A hardware phone keypad has 12 standard keys that also have emoji representation: 0️⃣ 1️⃣ 2️⃣ 3️⃣ 4️⃣ 5️⃣ 6️⃣ 7️⃣ 8️⃣ 9️⃣ #️⃣ *️⃣ . They are special in that they are actually using the standard Basic Latin digits and punctuation marks, followed by an (optional) variation selector and a (mandatory) combining character, U+20E3 Combining Enclosing Keycap. Many other emojis are represented in the same button style, depending on the vendor, e.g. media playback and navigation controls: ▶️ ⏸ ⏯ ⏹ ⏺ ⏏️ ⏭ ⏮ ⏩ ⏪ ⏫ ⏬ ◀️ 🔼 🔽 🔀 🔁 🔂 🔄. It should be possible for authors to request this style for all symbols that regularly appear on key tops, simply by using U+20E3: ▶⃣ ⏸⃣ ⏯⃣ ⏹⃣ ⏺⃣ ⏏⃣ ⏭⃣ ⏮⃣ ⏩⃣ ⏪⃣ ⏫⃣ ⏬⃣ ◀⃣ 🔼⃣ 🔽⃣ 🔀⃣ 🔁⃣ 🔂⃣ 🔄⃣.
The basic calculator keys are already available as emojis, ➕ ➖ ➗ ✖, and thus could use the combining keycap without any changes necessary: ➕⃣ ➖⃣ ➗⃣ ✖⃣. (Actual support for that is lacking, of course, and the results are awful.) Other operators would probably need VS-16, which are not yet in emoji-variation-sequences.txt, or U+20E3 would need to become an emoji.
Specific References
key toptemplateProposals