[Atrix 4G Android Development] jjwatmyself:
According one of my preferred DNS providers:

Default Server: BITSY.MIT.EDU
Address: 18.72.0.3

> h-slp.mnc410.mcc310.pub.3gppnetwork.org
Server: BITSY.MIT.EDU
Address: 18.72.0.3

*** BITSY.MIT.EDU can't find h-slp.mnc410.mcc310.pub.3gppnetwork.org: Non-existent domain
> supl.google.com
Server: BITSY.MIT.EDU
Address: 18.72.0.3

Non-authoritative answer:
Name: mobile-agps.l.google.com
Address: 74.125.127.192
Aliases: supl.google.com

So although h-slp.mnc410.mcc310.pub.3gppnetwork.org is not accesible from the public Internet, this doesn't mean that the mobile provider DNS (AT&T in my case) does not have a record pointing to an IP on their DNS server for mobile Internet devices...

So I then tested on the mobile:

Found?: Yes
NS:
Host: [URL="http://h-slp.mnc410.mcc310.pub.3gppnetwork.org/"]h-slp.mnc410.mcc310.pub.3gppnetwork.org[/URL]
Date: 2011-06-07 10:13:29 pm
Type: ANY
Run time: 2s378ms
Class: IN

; Screaming NetTools 2.1
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11292
;; flags: qr rd ra ; qd: 1 an: 1 au: 2 ad: 0
;; QUESTIONS:
;; [URL="http://h-slp.mnc410.mcc310.pub.3gppnetwork.org/"]h-slp.mnc410.mcc310.pub.3gppnetwork.org[/URL]., type = ANY, class = IN
;; ANSWERS:
[URL="http://h-slp.mnc410.mcc310.pub.3gppnetwork.org/"]h-slp.mnc410.mcc310.pub.3gppnetwork.org[/URL]. 14 IN A 209.183.51.114
;; AUTHORITY RECORDS:
[URL="http://mnc410.mcc310.pub.3gppnetwork.org/"]mnc410.mcc310.pub.3gppnetwork.org[/URL]. 300 IN NS [URL="http://ns1-silb.mycingular.net/"]ns1-silb.mycingular.net[/URL].
[URL="http://mnc410.mcc310.pub.3gppnetwork.org/"]mnc410.mcc310.pub.3gppnetwork.org[/URL]. 300 IN NS [URL="http://ns2-silb.mycingular.net/"]ns2-silb.mycingular.net[/URL].
;; ADDITIONAL RECORDS:
;; Message size: 133 bytes
;; Query time: 2378 ms
;; SERVER: <default>

This shows that AT&T have implemented this and does resolve.

Another one referenced with rave reviews is:

> supl.nokia.com
Server: BITSY.MIT.EDU
Address: 18.72.0.3

Non-authoritative answer:
Name: default.nokia.supl.geodns.fi
Address: 83.150.75.211
Aliases: supl.nokia.com
nokia.supl.svc.ovi.com
nokia.supl.geo.geodns.fi

In terms of performance, the next consideration is latency... so I pinged all three from my mobile and the results are interesting!

Found?: No
Run time: 5s758ms
Ping type: Advanced
Host: [URL="http://supl.google.com/"]supl.google.com[/URL]
Iface:
Date: 2011-06-07 10:16:31 pm

PING [URL="http://mobile-agps.l.google.com/"]mobile-agps.l.google.com[/URL] (74.125.127.192) 56(84) bytes of data.
64 bytes from [URL="http://pz-in-f192.1e100.net/"]pz-in-f192.1e100.net[/URL] (74.125.127.192): icmp_seq=1 ttl=46 time=459 ms
64 bytes from [URL="http://pz-in-f192.1e100.net/"]pz-in-f192.1e100.net[/URL] (74.125.127.192): icmp_seq=2 ttl=46 time=500 ms
64 bytes from [URL="http://pz-in-f192.1e100.net/"]pz-in-f192.1e100.net[/URL] (74.125.127.192): icmp_seq=3 ttl=46 time=434 ms
64 bytes from [URL="http://pz-in-f192.1e100.net/"]pz-in-f192.1e100.net[/URL] (74.125.127.192): icmp_seq=4 ttl=46 time=448 ms
64 bytes from [URL="http://pz-in-f192.1e100.net/"]pz-in-f192.1e100.net[/URL] (74.125.127.192): icmp_seq=5 ttl=46 time=435 ms
--- [URL="http://mobile-agps.l.google.com/"]mobile-agps.l.google.com[/URL] ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4000ms
rtt min/avg/max/mdev = 434.782/455.727/500.510/24.138 ms
Done!

Found?: No
Run time: 7s233ms
Ping type: Advanced
Host: [URL="http://supl.nokia.com/"]supl.nokia.com[/URL]
Iface:
Date: 2011-06-07 10:17:02 pm

PING [URL="http://default.nokia.supl.geodns.fi/"]default.nokia.supl.geodns.fi[/URL] [URL="tel:%2883.150.75.211"](83.150.75.211[/URL]) 56(84) bytes of data.
64 bytes from [URL="http://pos.svc.ovi.com/"]pos.svc.ovi.com[/URL] [URL="tel:%2883.150.75.211"](83.150.75.211[/URL]): icmp_seq=1 ttl=112 time=586 ms
64 bytes from [URL="http://pos.svc.ovi.com/"]pos.svc.ovi.com[/URL] [URL="tel:%2883.150.75.211"](83.150.75.211[/URL]): icmp_seq=2 ttl=112 time=550 ms
64 bytes from [URL="http://pos.svc.ovi.com/"]pos.svc.ovi.com[/URL] [URL="tel:%2883.150.75.211"](83.150.75.211[/URL]): icmp_seq=3 ttl=112 time=515 ms
64 bytes from [URL="http://pos.svc.ovi.com/"]pos.svc.ovi.com[/URL] [URL="tel:%2883.150.75.211"](83.150.75.211[/URL]): icmp_seq=4 ttl=112 time=509 ms
64 bytes from [URL="http://pos.svc.ovi.com/"]pos.svc.ovi.com[/URL] [URL="tel:%2883.150.75.211"](83.150.75.211[/URL]): icmp_seq=5 ttl=112 time=500 ms
--- [URL="http://default.nokia.supl.geodns.fi/"]default.nokia.supl.geodns.fi[/URL] ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4411ms
rtt min/avg/max/mdev = 500.710/532.552/586.832/31.911 ms
Done!

Drum roll please....

Found?: No
Run time: 7s508ms
Ping type: Advanced
Host: [URL="http://h-slp.mnc410.mcc310.pub.3gppnetwork.org/"]h-slp.mnc410.mcc310.pub.3gppnetwork.org[/URL]
Iface:
Date: 2011-06-07 10:15:42 pm

PING [URL="http://h-slp.mnc410.mcc310.pub.3gppnetwork.org/"]h-slp.mnc410.mcc310.pub.3gppnetwork.org[/URL] (209.183.32.149) 56(84) bytes of data.
64 bytes from [URL="http://209.183.32.149/"]209.183.32.149[/URL]: icmp_seq=1 ttl=121 time=103 ms
64 bytes from [URL="http://209.183.32.149/"]209.183.32.149[/URL]: icmp_seq=2 ttl=121 time=127 ms
64 bytes from [URL="http://209.183.32.149/"]209.183.32.149[/URL]: icmp_seq=3 ttl=121 time=120 ms
64 bytes from [URL="http://209.183.32.149/"]209.183.32.149[/URL]: icmp_seq=4 ttl=121 time=127 ms
64 bytes from [URL="http://209.183.32.149/"]209.183.32.149[/URL]: icmp_seq=5 ttl=121 time=127 ms
--- [URL="http://h-slp.mnc410.mcc310.pub.3gppnetwork.org/"]h-slp.mnc410.mcc310.pub.3gppnetwork.org[/URL] ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4004ms
rtt min/avg/max/mdev = 103.555/121.372/127.764/9.301 ms
Done!

WOW!! h-slp.mnc410.mcc310.pub.3gppnetwork.org is the better choice for AT&T in my opinion.

Obviously this is provider specific, so if you are a world phone user that needs AGPS, using an internet accessible AGPS server is the way to go, otherwise I would recommend sticking with stock in this case.

Also, does 'Enable Assisted GPS' duplicate 'Use wireless networks' which states 'Location determiend by Wi-Fi and/or mobile networks. This makes me 'think' it might be AGPS plus wifi positioning...

In summary... is AGPS (plus wifi GPS) already implemented and optimized on the Atrix? I'm leaning towards the yes side of the fence on this one.