Switching between internal and external antennas

A system, comprising:

• an antenna configured to communicate wirelessly transactions with transaction terminals;
• a connector connected to the antenna and configured to connect a transaction card to the antenna in response to at least insertion in the system;
• a housing enclosing at least a portion of the antenna and at least a portion of the connector and including one or more elements that form an opening for receiving the transaction card, the housing is substantially rectangular and includes a first portion with a first thickness and a second portion with a second thickness different from the first thickness and at least the thickness of the transaction card;
• and
• the transaction card comprising:
• a mobile interface that connects to a slot of a mobile host device;
• a communication module that wirelessly communicates Radio Frequency (RF) signals with retail terminals;
• secure memory that stores user credentials and a payment application used to execute financial transactions with the retail terminals, the user credentials and the payment application associated with a financial institution;
• a user-interface module that presents and receives information through a Graphical User Interface (GUI) of the mobile host device;
• and
• a processing module that executes the payment application using the user credentials in response to at least a transaction request and transmits at least one transaction response to the retail terminals based, at least in part, on the executed payment application.