I am looking for a reasonably priced solution to make VOIP calls by
using either SIP or Skype over a wireless network without losing the
PSTN line . First I describe the setup:
At home I have a wireless network with Router WRT54G (Hyperwrt
firmware) which is exploiting the neighbours' internet connection
through WDS-AP setup (don't worry, it is with his concensus). I hence
do not have my own wired internet connection. It uses WEP encryption
(If you know how to make it use WPA encryption this would be great, in
my casae it just does not connect, and I looked for hourse on the
linksysinfo.org forums)
The phone line is using a wireless DECT phone by Simenens linked to
its base (not one that can connect to the M34-USB). The phone can
connect to other Base stations without problems.
I am looking for the following possibilities or perhaps you have other
ideas. For this I need the possible products and if necessary special
software tweaking. In general, most important is multiple SIP, then
PSTN connectivity, then Skype.

Best solution would be:
Have a Wifi-phone with GSM that supports multiple SIP accounts, each
one can be activated by a prefix like #1, #2, #3 (I am using mainly
Sipgate as provider, but have also a US, an Italian and a Belgian
account). The softphone solution X-Lite support multiple SIP accounts
simultaneously. This is what I was thinking about. A full Skype
support would also be nice which allows incoming and outgong calls to
the Buddies. Probably highly expensive.

Other possibilities might look like this:
WiFi phone without GSM but with same SIP and Skype features. The Wifi
phone will cost a bit, I guess

A Router that serves as a SIP-Router (but multiple SIP accounts are
crucial) on which to put also the Skype software. Might the WRT54GP2
be useful? What other cheap and good ones are there? I would then
connect the DECT base to the router via an RJ11 jack. (What does such
a router cost? I guess it would then either replace the WRT54G I
currently have or would need to go into one of the WRT54G's LAN plugs.

My own router (WRT54G) with DD-WRT firmware and a wireless phone that
supports multiple SIP and Skype. (Again the cost of a wireless phone)

My own router (WRT54G) with DD-WRT firmware (does DD-WRT support
multiple SIP accounts) and an adapter to convert the Ethernet
connection (RJ45) to a PSTN one (RJ11) to which I would connect the
DECT Base (can this be a simple adapter?). Regarding Skype, I would
need to deal without it. How could I connect to the normal landline
PSTN (Costs seem to be only those of the adapter, but no Skype and no
PSTN)

The WRT54G with the current firmware (Hyperwrt) and an ATA connected
to one of the LAN ports, to which I would then connect the DECT Base
and phone (which ATA can deal with multiple SIP accounts? Is there
one, that could run Skype aswell?, it would also be nice to maintain
the PSTN phone line active like the Grandstream Handytone 486, they
call it PSTN-Pass-through, but that one dows not support multiple SIP
accounts). I saw a Zyxel Prestige 2002, but if I understood correctly,
it can only assign a single SIP account to max. 2 FXS ports.
http://www.zyxel.com/product/model.php?indexcate=1092126124&indexFlagvalue=1075687935.
Mediatrix ATA's are not for home use (extremely expensive), but
perhaps the SIpura SPA line is supporting what I am looking for.

I think from softphone side, the most integrated product that comes
close to what I am looking for is Jajah www.jajah.com, but it is a
softphone

Related issue: Is there a solution for the laptop via PCMCIA card or
USB to have a Laptop Dect-Base that allows to connect a DECT phone
(after registration to that base obviously) which could do multiple
SIP and Skype. The solutions by Siemens M34-USB
http://www.engadget.com/entry/1234000290030751/, the Dualphone
http://www.dualphone.net/ or www.greengate-solutions.de
http://www.greengate-solutions.de/index.php?id=13 satisfy the need
only partially: The first two work with Skype and PSTN, the second one
with a single SIP account. Solutions like www.pcphoneline.com are
nearly unbearable.

My sources up to now were mainly woip-info.org, the sites of the named
companies (Grandstream, Zyxel, Sipura,...), www.linksysinfo.org for
the router and Skype forum.

If you can resolve me this issue I would really be very very happy.
See the amount for that as well.
Cheers

If you have a spare PC, or a Linux box that's not doing much, you
could setup the free "Asterisk" VoIP PBX and use it as your "SIP
Router". This would enable you to make a "Dialplan" so when you call a
certain number, that call is routed out to a certain SIP account. So,
for instance, if you call +32 xxxxxxxx, Asterisk will contact the VoIP
Provider you have defined for Belgium and ask it to call the number
xxxxxxxx.

The only GSM + Wifi phones I have seen are the PAESYS GTEK PWG 500
(http://www.paesys.com/en/GSM_Wi-Fi_phone_for_SIP_voice_and_data_GTEK_PWG500.htm)
and the Nokia E60 (http://www.europe.nokia.com/nokia/0,8764,81338,00.html),
though the E60 doesn't say what VoIP system it uses.

Both of these phones, however, are not available yet. There are,
however, several Wi-Fi SIP phones, one or two of which support WPA as
well as WEP.

To connect the system to the PSTN, you can get a TDM04B from Digium
(http://store.digium.com/product_view.php?category=17&product_code=RTDM04B),
which supports up to 4 phone lines (Or, if you can find a distributor
in your area, try asking for the TDM01B, which only supports one line,
and is much cheaper). This is made to interop with Asterisk, so it
should work perfectly for what you want.

As for the Laptop question, I can't see why such a solution would be
needed. If you were to operate a Wi-Fi handset (As discussed earlier),
it would operate independantly of any computers, talking directly with
it's defined SIP server over the wireless link. There would, in this
instance, be absolutely no need for a connection, USB or otherwise, to
any kind of PC. If it's a matter of accessing your home setup from
away on the road, you could use a regualr phone ATA to connect to your
local Asterisk server, which would need port 5060 forwarded to it
through your firewall (If that's what you decide to go with), or just
to connect directly to your SIP provider.

I hope this helps some.