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Do you want this client to have full rights to the Spanish speaking Mexican market? If so then you can use hreflang, this will mean any time anyone is searching in Spanish in Mexico Google will show Flintel instead of Teletrac. If not then I would be very cautious of linking to each other Googlebot would see those as paid links unless they are all marked as nofollow. hreflang can always be undone and it can happen very quickly, I have made changes and seen dramatic results in 48hrs. Just make sure you set Teletrac as x-default so that all other traffic goes to Teletrac.