Line type lookup
Definition
A check that tells an app whether a number is mobile, landline or VoIP, and often which carrier owns it.
Line type lookup, explained
A line type lookup is a query an app sends to a phone data provider when you enter a number. The response typically says whether the number is mobile, landline, VoIP or toll-free, and often which carrier or provider it belongs to. Platforms use this to decide whether to send a code at all. Many block VoIP numbers outright, and some also reject landlines because they cannot receive SMS. This is why a Google Voice number can fail instantly on one app even though it works fine for texting. The data is not always perfectly current, so results can occasionally be wrong, especially for recently ported numbers.
Related terms
VoIP number
A phone number that runs over the internet rather than a mobile carrier's SIM, such as Google Voice or TextNow lines.
Non-VoIP number
A phone number issued by a mobile carrier for a SIM, so line type checks report it as mobile rather than VoIP.
Number porting
Moving your existing phone number from one carrier or provider to another so you keep the same number.