The problem is that AutoFill will only ask to remember account information if it is enabled in Settings -> Safari, and if you visit the login site in Safari itself instead of the logon screen (which is obviously also Safari, but not advertised as such).

The trick is then to trick your Wifi in not triggering in showing the logon form, but have the Wifi connected and surf to any site to get the logon screen working.

You can do it by disabling Auto-logon on your Wifi:

1. Disable Auto-Login in WiFi settings for given network
   • go to Settings app
   • select “Wi-Fi”
   • tap on the blue “>” icon to the right of your network
   • disable “Auto-Login”
2. Start Safari and surf to any site. The Wifi authentication page should pop up. Log in manually. If AutoFill is enabled including “Names & Password”, logging in prompts you to remember the login.
3. Re-enable Auto-Login for your network (same as step 1, but enabling “Auto-Login”)

Added february 7, 2012:

Ryan C. was kind enough to let me know by email that the above procedure also helps you out when your password has changed and you need to reapply the new password in the phone’s memory. As the Auto-Login is enabled, it will never kick in the procedure to recognize you tapped in a new password, and you will have to retype the new password over and over. By going to the 3 steps above you get again a prompt to save your updated password, and you’re then set to go with your new password.

The Intravee is an innovative piece of hardware that enables BMW’s of the previous generation to accept Ipods as sound source, and use the radio and steering controls to navigate through the Ipod’s structure.  This Intravee enables E39 5-series, E46 3-series, the first model of X3′s and the first model of Z4 roadster and coupe owners to enjoy their Ipod in their car.

De Intravee is een innovatief stukje hardware dat het mogelijk maakt om in BMW’s van de vorige generatie toch een Ipod te gebruiken als muziekbron.  Zo past deze Intravee eenvoudig in alle E39 5-reeksen, de E46 3-reeks, de eerste reeks X3′s en de eerste modellen Z4 roadster en coupe.

The Intravee is actually not an Ipod-adapter per-se: The Intravee only acts as an adapter between the BMW media protocol, and the AlpineNet protocol to transmit commands and track info back and forth.  The actual Ipod-adapter is something such as the Alpine KCA-420i which enables an Ipod to talk AlpineNet and vice-versa.  Keep in mind that the KCA-420i has limitations such as being only able to show up to 511 albums and 511 artists, which means that if you take your whole collection of music on the road, you might not be able to select ZZ Top as artist out of the menu.

Contrary to the other models which have cd changers and navigational computers mounted in the trunk compartment, the electronics of a Z4 roadster are placed in between the two seats, under the covering that runs out of the gearbox and drivetrain tunnel.  This hampers the installation of the Intravee and the Alpine adapter, in such a way that large parts of the interior of a Z4 roadster need to be removed before access is gained to the existing cabling to enable the Ipod adapter.

As a sort of reference, I have gathered the Alpine CD Changer Installation documentation from BMW which describes how to install an Alpina CD Changer, including removing and restoring the interior parts that hide the electronics in between the seats.  This gives access to the cables necessary to connect the Intravee and the Alpina KCA-420i adaptor as described in the Intravee Quick Install Guide.

Update: Another option is to access the necessary cables through the trunk, as explained in this thread on z4-forum.com

De Intravee is eigenlijk niet de eigenlijke Ipod-adapter: De Intravee is een adapter die het BMW media protocol vertaalt in het AlpineNet protocol en vice-versa om commando’s en trackinformatie uit te wisselen.  De eigenlijke Ipod-adapter is vaak de Alpine KCA-420i die de Ipod laat praten met AlpineNet en vice-versa.  Denk eraan dat de KCA-420i een limiet van 511 artiesten en 511 albums heeft bij het gebruiken van de zoekfunctie, en je bij een volle Ipod met je hele muziekcollectie mogelijks niet meer tot ZZ Top geraakt als artiest.

In tegenstelling tot alle andere modellen, waarbij bekabeling, cd-wisselaar en navigatiecomputer in de koffer gemonteerd zijn, is al deze electronica in een Z4 roadster enkel beschikbaar tussen de twee zetels, in een uitloper van de middenconsole.  Dit vereenvoudigd de installatie niet, aangezien hiervoor grote delen van het interieur gedemonteerd moeten worden om toegang te verschaffen tot de bestaande bekabeling.

Als een vorm van referentie heb ik de Alpine CD Changer Installation documentation teruggevonden waarin staat beschreven hoe een cd wisselaar kan ingebouwd worden, inclusief het demonteren en monteren van de interieuronderdelen.  Dit geeft toegang tot de nodige kabels die beschreven zijn in de Intravee Quick Install Guide om succesvol de Intravee, Alpine KCA-420i en bijgevolg de Ipod te laten werken.