Currently we can support receiving text messages on your existing phone number if that number is a landline . VoIP and mobile numbers are not supported. If you're unsure what kind of phone number you have, contact support and we'll look up the number for you.
We also can port any existing phone number to our service, but when ported the number will only be useful for texting and will not be able to be used for voice service. This is not a good option for your existing voice line, but might be an option if you have obtained a set of similar number (Ex: "Call us at 555-555-1000 or text us at 555-555-1001").