How to service American client while living in Baja?

Where in Baja?  I haven't moved yet but have explored some options for Rosarito area. 

Mail: you can have it sent to a San Diego address and either drive over and pick it up or have a pickup service bring it to Baja.  Then you go to their location and pick it up.  I know in Rosarito there are a couple of places that will pick up at a San Diego address and bring it over.  You can keep your current So CA address and have it forwarded to the San Diego address.  Downside is it will probably take time for it to get to you.   

Telephone shouldn't be an issue, either use your US cel number and get a plan that includes Mexico or get a VOIP (Magic Jack or Vonage) keep your current landline and have it ported over to the VOIP.  It's been a few years, but we ordered a Vonage system with a local US area code number shipped to our CA residence.  We then sent it over to our son who was in the Army stationed in Korea.  He plugged it in to his computer and it was just like calling across the street here in CA.   

Internet shouldn't be a problem it's just like in the USA.  I think Izzi has a pretty good plan that includes TV service also.