What connector is similar to U.FL but has no pin?
It's a special switched connector for testing or using external antennas.  Notice that there is a trace on both sides of the connector, but only one side on the u.fl connector.  When you plug a test connector into the jack, it actually disconnects the signal flowing through it and routes it out the test connector instead.  They show up all the time in wireless routers and the like because they can be used to perform accurate tests on the radio with the antenna disconnected before it ships.  They can also be used to add an external antenna to a device by bypassing the internal antenna.  This is one series of this type of connector:

http://www.ttiinc.com/object/Murata-Switch-Connectors-HSC-RF-Coaxial.html