Vodafone Germany owns Arcor (an ADSL provider in Germany), so I figure they're a good example to look at. They've got a cordless VoIP phone for home (or any wireless access point) which roams onto the GSM network when away from wireless.
The translation is roughly:
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With the new Arcor-Twintel telephone, you can simply take your flatrate with you. It's a landline and mobile telephone in one. Where ever a WLAN access point is available, you can use your flatrate. When there's no WLAN you telephone with the Twintel as a mobile phone just like you're used to.
New: The Landline-mobile
Landline and mobile telephone in one deal.
* A normal telephone for Landline and mobile
* Also when you're in the office, at friends, or out and about with available WLAN - you can use the Arcor flatrate
* Your own landline and mobile number for each device
* When a WLAN is not available, it works like regular mobile telephone
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I think this is the future... (well, a small part of it :).
