Reference the attached screenshot. The logo generally will be displayed small, horizontally in the upper left corner IN PLACE OF the word "Jack".
T3 can by stylized but should be easily readable (for example, avoid "is that a 3 or a B?"). The design style throughout the site is "flat" with a color palette that resembles Google+ or Apple.
Of the "logos I like," the "ca" one is my favorite. Stylized but design elements aren't adding extra height to the logo and uses colors in our general palette. Don't let the sample logos though constrain thinking to narrowly. There weren't a lot of good examples I could find online of letter mark logos.
I also checked "pictorial mark" in case there's a natural way to incorporate an icon of a phone or coiled phone cable into or between the letters. Leaning toward a letter mark but if you're inspired to put in phone imagery into the logo, we're open to ideas.
Si usa tipos de letra que requieren licencia, confirme que el cliente esté de acuerdo con su uso. Por motivos de licencias, es mejor proporcionarle a su cliente información sobre cómo adquirir el tipo de letra en lugar de proporcionarle los propios archivos.
El texto en logotipos debe convertirse a letras sin relleno.