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How to format your contact list for Twilio
Twilio is one of the more reliable SMS platforms on the market, but its bulk import has the same trap every SMS provider has: the phone numbers in your iPhone aren't in the shape Twilio expects. This guide walks you through the fix.
What Twilio needs
Twilio's Messaging API requires E.164 (+15555550100). Numbers without a country code get rejected at send time, not at upload time.
You'll want a CSV with one row per subscriber, a Phone column in E.164 format, and (optionally) a Name column. Some Twilio features require extra columns. Consent timestamp, opt-in source. But the core import is just phone + name.
Producing the CSV from iPhone
Three paths: Mac Contacts > Export > CSV (then reformat the phone column), iCloud.com > vCard > convert externally to CSV, or Pluck on iPhone with E.164 export selected.
Pluck's E.164 format option strips local prefixes, adds the country code, and validates against libphonenumber before export.
Why E.164 matters
E.164 is the international standard for phone numbers: country code prefix (+1, +44, +234, etc.) followed by the national number, no spaces, no parentheses, no dashes. Twilio's deliverability depends on every number being in this exact form. A 'pretty' local format like (415) 555-2671 will either get auto-corrected (often wrongly) or skipped entirely.
See our guide on E.164 for the full mechanics. The short version: prepend +1 for US/Canada, drop the leading zero for most other countries, then add the country code.
Country-specific gotchas
Numbers from different countries need different normalization rules. UK numbers drop the leading 0 (07700 900123 becomes +447700900123). Italian landlines keep the leading 0. Brazilian mobile numbers got a 9th digit added in 2016. For a fuller picture, see How to group your contacts by country.
Pluck handles the normalization per country automatically. Export a single international file or export one CSV per country and run separate Twilio campaigns per region. The per-country split is useful for opt-in compliance, since SMS regulations differ wildly across borders.
Deduplication before upload
Most contact lists have 10-15% duplicates, often the same person stored under two different number formats. Twilio will charge you separately for each (and possibly trip carrier abuse filters with too many sends to the same person). Run dedupe before upload. How to find duplicate contacts on iPhone walks through it.
After the import
Once Twilio has your subscribers, the contact list in iPhone and the one in Twilio drift apart over time. If you add a new contact on your phone, it won't appear in Twilio without a re-export. Most senders re-upload monthly or quarterly to keep the list in sync.
Get Pluck for iPhone
Pluck does the steps in this guide on your iPhone, with no server, no account, and no analytics. Group your contacts by country, find duplicates the iOS tool misses, and export to CSV, Excel, TXT, or vCard.