Having trouble creating new accounts | Problemas creando cuentas nuevas

Some phone numbers are not taking, it is unrelated to the country because I've been able to have others from the same country create accounts. But it's been 3 times already someone tells me they are unable to create the account with their phone number...can anyone tell me if there are any requirements? Honestly I don't feel like trying to bring more people over if all I am doing is getting them excited to then disappoint them.

Ya tres personas me han dicho que no han podido crear cuenta en Steemit porque se trancan en el numero de telefono. Hay algun requerimiento con los mismos? No quiero emocionarles con Steemit para despues desilucionarles.