Guides
How to get a phone list into a state where your campaign does not waste money on numbers that were never going to answer.
No guide matches that.
Why libphonenumber returns FIXED_LINE_OR_MOBILE for US numbers
getNumberType() will not tell you whether a US number is mobile, and that is correct behaviour. What the library can know, what its carrier mapper returns after a port, and the three ways to get the answer.
NPA-NXX explained: how a US phone number is actually allocated
What NPA and NXX mean, why the seventh digit is an allocation boundary rather than part of the line number, and what block data can and cannot tell you.
What E.164 is, and why your list probably isn't in it
E.164 is the international format every SMS gateway and dialler expects. Here is the rule, the four mistakes that break it, and how to convert a messy export without guessing.
How to clean a phone list before an SMS campaign
A sequenced checklist for scrubbing a phone list before you send: deduplicate, normalise, drop unallocated numbers, remove landlines, then enrich only what is left.
Phone number line type: how to tell mobile from landline and VoIP
Line type decides whether an SMS arrives or is silently discarded. How it is derived from a numbering plan, why the NANP makes it hard, and what number portability limits.
How to clean a phone list before importing it to Klaviyo
Klaviyo rejects phone numbers that are not in E.164 and charges you for SMS to landlines. Here is how to prepare the file so the import runs clean the first time.
What phone validation actually costs
Published per-lookup API rates, worked examples on a 100,000-row list, and where a local numbering-plan pass changes the arithmetic.
Two phone validation APIs disagree with each other 27% of the time
We tested our offline validator against Twilio Lookup and Veriphone on a pre-registered sample of 800 US numbers. The most interesting result was not about us: the two paid APIs disagree with each other more than a quarter of the time.
Get told when the numbering data moves
Carrier block reassignments, line-type corrections and what changed in the numbering plans we ship. Sent when there is something to say, which is not often. Your address is used for this and nothing else.