Last of the Time Lords
When Martha Jones becomes an ongoing companion to the Tenth Doctor in "42", he gives her phone, the BenQ-Siemens EF81, a similar upgrade. This phone, however, is upgraded by the Doctor's sonic screwdriver, and the feature itself is referred to as "Universal Roaming". Martha's phone has the Archangel network logo on its display, the significance of which is revealed in "The Sound of Drums". At the end of the episode "Last of the Time Lords", Martha gives her phone to the Doctor, so she can contact him if trouble occurs.