Yeah, so they're 2 completely different paradigms that can be linked together.
With multiple locations, even in the same area code, in CM you have location based ARS, so users in location 1 pick ARS matches in location 1 to routes that map to trunks in location 1, and not the trunks at location 2 across town.
Now, you can use the IP-network-map to associate IPs to regions, and regions to locations, or you could hard-code the location on page 1 of the station form - unless they're SIP phones - so you'll eventually have to get used to using the network map.
From the SM perspective, its IP address doesn't need to be defined in the network map to a network region. If you think about it, SM is never the "end point" making the call, it's just a pass-through for a set or a trunk. You can give the SIP sig group's far end node a network region - and that's used exclusively for what codecs CM will offer on an invite, but has no other bearing on things.
It's also important to understand how location is determined. On both CM and SM, for an incoming SIP invite, they will both look at the IP address of the oldest (furthest down) via header in the invite.
So, suppose you had no TDM trunks - all SIP - but you had H323 phones. A H323 phone calling 911 would have the oldest via header being the IP of the H323 phone. You might have carrier PSTN SIP trunks on a SBC for everything, but you might also have a little audiocodes analog gateway at each site with a copper trunk for 911. In that case, SM would see 911 called "from" the location of the H323 phone and could trigger on routing to say "send this call to the audiocodes at this guy's location in NY so it calls NYPD out the copper trunk there"
Take the opposite situation: all SIP phones, all PRI trunks. You have sites all across the country and only 1 SM. It stands to reason that all those SIP phones hitting CM are coming from the same SM IP, but you'd want the SIP set's IP address to determine its location just like a H323 would. CM, like SM, will look at the oldest via header of that invite from the phone-->SM-->CM and know the IP of the phone calling and associate it to the appropriate network region.
For your case, I'd just be worried about what happens when someone calls 911 and how important that is to you.
You said you're all in the same area code - is that also the same PSAP area by chance?
Do you have anything fancier than just "main billing number = 123 main st" per site and that's all that gets to the PSAP?
Are you dead certain that you can avoid location mixups when people call 911 from those wireless phones?
Does Bob have his extension at his desk and on his wireless phone and he goes in the warehouse sometimes and when he calls 911 and reception sees it on the console they'd direct the ambulance to Bob's desk and not the warehouse?
That's the Nth degree of uptight i'm talking about with the things that are accounted for in a solid design that accounts for all use cases. It might be overkill in the context of your little itty bitty question, but the examples help illustrate the configuration elements in CM and SM, why they're there and how to use them. That, and it's all stuff that'll get asked one day if someone ever gets a misdirected 911 call - the network guy adds a new wifi subnet you didn't know about that defaults to location 1 instead of location 2 and you call a different PSAP in the same area code but on the west side of town instead of the east side of town or whatever.
And if it was just a plain old office environment, you'd have probably bought DECT headsets on deskphones. Wireless to me means something that isn't a static fixed work area and might well have some extra safety requirements that you could use a little CYA for. Either just to make yourself look good, or because someone might actually count on that config in a life or death situation.
